Hard Pool Water: Removing Calcium Scale

Many parts of the United States have hard water which can leave calcium deposits at the waterline, or calcium crystals or thin sheets of calcium scale on the pool walls and floor.

After defining the cause of pool scale and ways to prevent scale problems in pools, we will cover how to remove scale from vinyl, fiberglass, and concrete pools.

Problems with Pool Water Hardness

 hard water map image by h2odistributors.com

In many parts of the country, tap water with hardness levels of 400-800 ppm is not uncommon. Elevated calcium levels, particularly when coupled with rising pH, can result in the formation of whitish scale or crystalline deposits on pool surfaces, including at the water line, inside pipes, or throughout the pool.

High water hardness may cause cloudiness or calcium stains as hard minerals combine with dirt and oils, precipitating out of solution.

Controlling Calcium Hardness in Pools

As opposed to removing calcium in pools, many pool owners opt to control the mineral build-up in pools. The primary method of control is to keep well-balanced pH and alkalinity levels. With a proper pH of 7.2-7.4 and Total Alkalinity of 80-100 ppm, high levels of calcium rarely become problematic.

Natural Chemistry Scale Free Scale and Metal Protection for Pools

Secondly, using a sequestering agent like Scale Free or Stain Away, will lock-up minerals (sequester) with a strong chemical bond, that will keep calcium from precipitating out of solution, to form scale or visibly cloud the water.

Avoiding the use of calcium-based sanitizers, such as Calcium Hypochlorite, is also recommended as a way to reduce calcium build-up. Lithium, Dichlor or non-chlorine shock can be used as alternative pool shocks, that won’t add calcium to the pool.

Reducing Calcium Hardness in Pools

To decrease pool hardness levels, explore methods for lowering calcium levels if controlling hardness becomes challenging.

Drain part of the pool, and refill with softened or low-calcium water from a home system or trucked-in. Captured rain water, which has 0 ppm of calcium hardness, has also been used by some as a means to reduce calcium levels. But there are other methods.

Reverse Osmosis Filtration

Amid water crises and droughts in the south and west, pool and spa owners often face restrictions on draining their pools. This rules out the Dilution Method for lowering calcium hardness. Innovative entrepreneurs have answered the call by operating mobile pool filtration units. Using huge truck-mounted reverse osmosis filters and water softening agents along with pH control, they can pump your entire pool through the truck a few times. The result is fresh and balanced pool water, with calcium hardness removed to an appropriate level.

Precipitate and Floc

ph increaser

There are still some old pool guys that insist on this method, but it can be risky. The idea is to carefully raise the pH with sodium carbonate or soda ash, to a point above 8.2, or off the scale. When conditions are right, the excess calcium in the water will begin to precipitate and visibly cloud the pool, turning it milky white. Then, using a flocculent like Aluminum Sulfate or PhosFloc, you drop all of the suspended particles to the floor, and vacuum it out to waste. Then lower the pH level back to around 7.4, and check your Alkalinity. Calcium Hardness can be lowered by dramatic amounts with this method, but you risk staining or calcium deposits on pool surfaces.

Cal Treat

Cal Treat is a product produced by United Chemical. It uses a form of Dry Acid to remove light scaling and reduce calcium hardness levels without draining, according to the manufacturer. Use one bottle per 15,000 gallons, to reduce calcium hardness below 400 ppm. Actual ingredients for the formula are a closely guarded secret, but some claim that it may have a form of phosphates. Reviews are mixed, for some people it seems to work well, and for others, the results were less than expected. Your mileage may vary.

Zeolite Filter Sand

zeolite filter sand

If you have a sand filter, you can replace regular pool filter sand with ZeoLite pool filter sand, which has the ability to trap the very tiny particles of calcium carbonate. It does this not by filtering out the particles, but by ion exchange. Calcium and magnesium ions are exchanged for sodium ions in the zeolite sand bed, with softens the water. The trapped calcium hardness is then simply backwashed out of the pool filter. Zeolite filter sand needs to have the ions refreshed after a few years, flushing it with a strong sodium solution, a Zeo Filter cleaner will restore it’s ionic charge.

Poolside Water Softening

Home water softening units can be set up next to the pool. Using a small pool pump or submersible pump, you can circulate the pool water through water softening filters that utilize sodium and ion exchange to reduce calcium levels. After the water is pumped through the water softener, a discharge hose pumps it back into the pool. A system large enough to handle a pool might set you back $500 or so. If your home already has a water softening unit, the outdoor spigots may not be connected to the system. Consider using the utility sink or laundry room sink for a more effective way to fill or refill the pool.

What Causes Scale in Pools?

Calcium carbonate scale can form along the waterline of the pool as evaporation increases during the summer. Scale itself is a white translucent color, but is often mixed with dirt and algae to appear darker.

Calcium crystals may appear as nodules on the pool surface, ladders, and light rings, or as crusty deposits in corners. Minerals like calcium commonly form ‘sheets’ of scale, covering the entire pool surface in a thin layer.

The most common cause of calcium scale in pools is the result of high calcium hardness, over 400 ppm, yet is triggered by high Alkalinity, high pH and high water temperatures. Some will tell you to drain the pool if over 400 ppm, but not necessarily!

The best way to control for the various elements leading to pool scaling is to perform a regular test known as the Langelier Saturation Index, or LSI for short. An LSI test determines a pool’s preponderance for scaling or etching. A pool is considered to have a balanced LSI when results are -0.3 to +0.3. Test results below -0.3 indicate a prevalence toward corrosion – and above +0.3 and your water is ‘scale-forming’.

The math is a bit complicated to calculate the LSI, but you can use the Pentair LSI Tool – just plug in your water test levels and it crunches the numbers for you! The tool is then used to see the effect of adjusting chemical levels.

How to Prevent Calcium Scale

Calcium scale often results from water chemistry interactions, preventable or circumvented with various prevention methods.

lower ph level
  • Use a sequestering agent to keep calcium locked up in solution, so it can’t precipitate into scaly deposits. Chemicals such as Stain Away or Scale Free sequester metals and minerals. But, only if you apply the regular maintenance doses every week or two.
  • Avoid calcium hypochlorite shock, which adds calcium to the pool. Use a non-chlorine oxidizer, or di-chlor pool shock.
  • Lower your pH and Alkalinity on the low end of the scale; a pH of 7.2-7.4 and Alkalinity of 80-90 ppm. High pH and Alkalinity create ideal scaling conditions.
  • Compute your LSI, a formula that computes your water’s propensity to scale. Negative results below 0.0 are best to avoid scaling. Pentair LSI calculator does the math for you.
  • Use a clarifier to seek out calcium particles and clump them together so that your pool filter can remove.
  • Brush the pool frequently to eliminate fresh scale, and vacuum or use the pool cleaner multiple times weekly to clear calcium dust and dirt.

How to Remove Calcium Scale

instant liquid acid

Calcium Scale can be removed with muriatic acid, or dry acid dissolved in water. A sponge works well for small areas or a flower watering can for larger areas. Don your lab glasses and gloves for acid removal of tile scale. It will fizz and bubble and emit noxious fumes as it dissolves the scale. Acid Magic or Instant Liquid Acid or even pH Decreaser can also be used as a safer acid to remove scale. Do not use household cleaners to remove pool scale, which add chemicals that don’t belong in your pool.

For swimming pools, the range of acceptable hardness levels is 200-400 ppm, although many suggest a tighter range of 180-220 ppm for plaster pools and 150-250 ppm for vinyl pools.

What about Efflorescence?

Efflorescence, a pool scale variant, arises from moisture in raised rock walls or beneath the pool coping stone, not the pool water. It can be seen coming out of mortar joints between stones on a raised rock wall, or can drip down onto pool perimeter tile, flowing from the mortar bed beneath pool coping stones.

Efflorescence can be slowed by using Clear Sealer on rock or brick faces, and making sure that pool caulking is maintained to keep water out of the expansion joint. For raised rock walls, applying a bitumen or similar waterproofing on the backside of the wall can be used to block the moisture seeping through the wall.

Calcium Deposits on Tile

Lower the water level to the bottom of the tile and use a putty knife or similar tool to help knock off the heavy stuff and break through crusty outer layers. Use Acid Magic or Instant Liquid Acid and apply with a thick brush, pour with a flower watering can, or spray from a spray bottle. Rinse with water after 1 minute; reapply if needed.

pumice stone

Use a pumice stone to remove scale deposits from pool tile with light scrubbing. A nylon bristle wheel or nylon brush cup on a (cordless) drill can be useful and safe to use, pumice wheels are also available. Avoid steel bristle cups and wheels to prevent damage to tiles or formation of rust spots on your pool floor.

Wet-Dry sandpaper can also be used for light scale on pool tile. Or, you can hire a local bead blasting service to come out and professionally remove the calcium on pool tiles. Many are now using magnesium sulfate, an inorganic salt that is less aggressive than bead or sand blasting.

Calcium Deposits on Plaster

White plaster pools often have unnoticed widespread calcium deposits due to their already white surfaces. Black or Grey plaster pools develop the same hazy calcium films but are quite noticeable. Darker colors can be restored with acid washing.

To remove nodules or crystals from the surface, you can start with a pumice stone, and see if you can manage to do the entire pool, sanding off the rough calcium bits. The pool could also be drained, to acid wash the surfaces, or possibly just pressure wash the pool. Small trouble areas can be smoothed with wet/dry sandpaper or a nylon wheel on a drill.

Remove Efflorescence on Pool Tile and Stone

Like calcium scale from pool water, efflorescence is calcium lime scale from grout between tiles or stones in a wall or water feature.

microcare acid magic

To remove tile scale on pools, first scrape off the heavy deposits with a small putty knife, then use a flower watering can to pour of Acid Magic or Instant Liquid Acid, full strength on the front lip of the coping, to run over the tile. Scrub the tile with a stiff brush if possible, then rinse off with a hose within 60 seconds. Repeat if needed, then raise the pool water pH and Alkalinity, now lower from the acid.

Moisture emerging behind tiles or stones through grout or mortar joints brings calcium, causing the issue. The same process that creates stalagmites.

Sometimes the moisture comes from the pool as shown below. Sealers can be used on the tile to provide an invisible barrier. To prevent efflorescence on larger stone or brick walls above water, consider sealing or redirecting water sources behind the wall.

Removing Scale on Vinyl Liners

While the slick vinyl liner surface minimizes calcium scale, deposits may occur when conditions permit.

Contrary to metal stains on liners, mineral scale is tactile, feeling rough and ‘scaly’ to the touch on your hands and feet. In severe cases, it can be rough, causing swimsuits to snag and discomfort for children with ‘pool toe.’

Stain Eraser

Remove vinyl pool scale carefully to prevent damage or a worsened appearance compared to other pool types. The Stain Eraser for vinyl pools is tough enough for stains and scale, and works great for small scale problems.

Lower the water level, spray white vinegar (with a few drops of dish soap) on vinyl pool waterline scale. Spray a few feet, then scrub the surface with a textured sponge or scrubber, then rinse off. Most visible scale will need an acid stronger than vinegar, however. Mix 4-8 oz. of Acid Magic or Instant Liquid Acid with water in a spray bottle, then repeat. Strong acid can remove tile patterns from your liner, so test in small areas and gradually increase the strength.

For all-over scale in a vinyl pool, an accepted treatment is to:

  1. Add a full dose of Stain Away or Scale Free to lock-up calcium scale.
  2. Lower the pH level to 6.5 for two days*, brushing the pool 2-3x per day.
  3. Return pH level to 7.4-7.6; continue with maintenance doses of Stain Away.

Controlling Pool Scale

Once you remove pool scale, how do you prevent it from coming back?

Sequestering agents keep calcium and carbonates in solution, preventing them from precipitating and causing issues. Replenish sequestering agents every week or two, as sanitizers and sun deplete them, ensuring ongoing protection.

Use Scale Free for effective control of pool scale by targeting calcium carbonate in pools.

78 thoughts on “Hard Pool Water: Removing Calcium Scale

  1. David Wayne

    The pool was Replastered in March of 2016. Now in 2020 am seeing calcium deposits over the bottom of the pool. The plaster in some areas are dirty looking. The service just put in a new filter (canister) which replaced the old filter which was not a canister. Soon after the filter was replaced the calcium deposits started to appear. The service never mentioned I had deposits. Only found out when searching for new pool service. Could the new filter have anything to do with it? Thank you

    • Hi David, filtration is not usually related to calcium deposits, I don’t think that is the cause. Calcium deposits can occur from a high pH and high calcium, or from heavy shocking – knocking the calcium out of solution. Regular use of a sequestering agent can help keep calcium in solution. Calcium scale is common, and exists in most pools, but is not very obvious, unless it mixes with dirt or other substances, making scale/stains. You could drain and acid wash the pool, that will remove the scale/stains and then start using a sequestering agent regularly, and keep a good watch on alkalinity/pH levels.

  2. Jim Penny

    I successfully reduced my Calcium hardness by half using sodium carbonate (soda ash) to precipitate out calcium carbonate then vacuuming to waste. The trick is to run the pump on recirc bypassing the filter then adding the soda ash from a bucket to different parts of the pool. If you dilute it too much, it doesn’t work because it needs the local pH to increase to drop out the calcium carbonate. Once it drops out, it doesn’t go back into solution. You can keep checking the total hardness as you do this.

  3. I had to drain my fiberglass pool for some repairs from the manufacturer, and noticed some heavy calcium buildup under the waterline. Since the pool is now empty, what is the best way to remove the scale?

    • Hi Marc, pick up a gallon of muriatic acid, and dilute it by adding equal parts to water in a clean spray bottle. You can also pour it on the wall from a small flower watering can. Let it fizzle for a minute and then hose off thoroughly with water. Neutralize the waste water with pH increaser, and then pump it out of the pool, quickly. You can also use products like CLR, but on a rag, wearing gloves, and also pump out wastewater.

  4. Misty Alafranji

    We have very hard water and have noticed a white sediment that settles to the bottom of our small 8ft above ground pool. It’s crystal clear until you get in and the sediment rises to the surface and clouds the water. Is this calcium? How can we clear it out? Help! Thank you.

    • Did you use a flocculent chemical? That is known to sink material to the floor, for ‘vacuuming to waste’. It could also be calcium however, from the hard water, or from using calcium based shock. In either case, you want to find a way to vacuum the pool, with an external pump or a submersible pump, or even a strong siphon. Or vacuum into the pump, but disconnect the return line from the pump and plug the wall, to flood the yard with waste water.

  5. Don Bellville

    Hello,

    Our water is very hard. Located in Maricopa AZ, 85138.

    20,000 gal Salt Water Pool is only 3 years old with glass beads in the plaster. Lots of water line buildup and now getting under water white growths. Pool was recently acid washed.

    Question: If money was no object, what could be done to eliminate these issues or immensely reduce them?

    I was told that we should not use water from the house as we have a slat treatment system for the internal plumbing. We use the outdoor water hose bib to fill the pool and the auto fill.

    I’ve read about dedicated water systems, RO systems etc…Money is always an object but it can’t be as much as a life time of chasing these issues.

    Please feel free to suggest any brand or particular systems to consider.

    Greatly appreciate any help.

    • Hi Don, many people live in hard water areas, like yourself, and they all share your problem of calcium deposits, very visible on the waterline tile, but not always so visible on white pool plaster, but it’s there… To reduce scaling, or the precipitation of calcium from the water:
      1. Maintain tight water balance, keep the pH and alkalinity in line, and on the low side, 7.2-7.3 pH, and 80-90 ppm Alkalinity.
      2. Avoid heavy shocking with chlorine if possible, as well as other major chemical changes to the water, which can ‘throw off’ some dissolved material, pushing it out of solution, where it floats around, until it deposits on the nearest suitable surface.
      3. Avoid using calcium hypochlorite pool shock, use di-chlor or non-chlorine shock instead
      4. Add fill water from a utility room sink or other source that IS connected to the home water softening system, as most outside spigots are not.

      As for #4, not sure why you can’t use the slat treatment system, not sure what that is.

      For removal of plaster scale, generally draining and cleaning is performed, an acid wash. For the tile line, you can also use muriatic acid, diluted and applied with a flower watering can or spray bottle, scrub and rinse. Don’t forget to adjust your pH and alkalinity if you use enough acid during cleaning tiles. You can then seal the tile or stone, to prevent future deposits. We carry a line of products that is designed for that – LayorCare, we have a “Heavy Calcium Releaser”, a “Cal Block” and Sealers. You can find them here: https://www.intheswim.com/c/new-chemicals

  6. edward jaanson

    In many of the comment replies, you mention to bring the ph to 6.8, and then let it stabilize at that value so it allows the break-down of calcium. Would it be harmful to just keep our ph level at 6.8, to prevent future calcium build-up?

    • Hi Edward, yes it can harm the soft and shiny pool surfaces. anything below 7.0 (neutral), is in the acidic range. 6.8 is not very acidic, but over time, it can etch and erode pool plaster or vinyl, or chrome and rubber materials. It is also a bit uncomfortable for skin and eyes. It will not allow a breakdown of calcium, but it does make chlorine more potent. To dissolve calcium scale underwater, the pH level would need to be much lower, perhaps 2.0-3.0, which is not feasible. Muriatic Acid can be used on tile and stone, above water level however.

  7. We had our pool resurfaced in March of 2019. The pool walls are very rough. The company we used insisted it was the pool surface we chose which was pebble aqua cool. Yes a larger pebble but in no way should be skinning knees and toes. I had the manufacture rep come look. He said install was good but pool had a lot of scale. He recommended to the pool surface contractor jacks magic stuff. Two treatments were done Supposedly. Poor communication from the owner/comany. Bottom line is he refuses to do anything about the surface. Sends email saying we have high phosphates. A) would high phosphates cause scaling
    B) would a phosphate treatment remove it?
    C) what does one do after paying almost 8k for a new surface and a contractor that refuses to even come see the problem for himself?

    • Hi there, phosphates do not contribute to scale, and phosphate removers don’t remove scale. High pH and high calcium levels will cause scale, among other things. Be sure that your pH level is maintained, as new plaster/pebble pools will rise steadily for a year. Jacks Magic products may not remove scale. If you want to be sure that it is scale, put on a mask, and dive down and look at it. Probably not an issue from the pebble job. The best way to remove scale, if Jacks Magic did not work would be to drain the pool and acid wash – or do a no-drain acid wash procedure.

  8. Nicole Lancaster

    Hi, our entire vinyl liner walls feel like sandpaper….our water is crystal clear and chemical levels are almost perfect…can u break it down in laymens term on how to remove this what appears to be scale. Exactly how do u lower pH and know if its within range to start treating the scale? How much of the solution should we use? Should I use scale free vs stain away?

    • Hi Nicole, I would first try lowering the pH to 6.8, by adding enough pH decreaser to get there. First check your current pH level, and you can use https://app.poolcalculator.com/ to find the exact amount of liquid acid or dry acid to use, to get to 6.8-ish, which is just slightly acidic. Then you will use a good stiff pool brush (like the ones with black bristles), or you can get in the pool with a stiff hand brush, and brush the pool, or use a soft plastic scraping tool, to knock off the nodules/crystals. Then I would use a sequestering agent like Scale Free or Stain Away to keep calcium scale in solution, and off the walls. You have to add it regularly – it depletes in 1-2 weeks.

    • Renee Connell

      We are having the exact same problem with our vinyl liner, this year. I was wondering if anyone has tried the process that’s being suggested below? And if so, what was the result? We lowered our PH to 7.0 (suggested in a different post that I found), used the Scale Free and brushed our pool several times but probably not as often as we should have. And so far, no luck. I was going to try dropping the PH to 6.8, as suggested in this post, and try scraping the grit off with a plastic scraper, but our liner is covered with this stuff and it is really stuck on there. So, I just wanted to see if anyone has had any success with this process or if it is more realistic to start saving for a new liner?

      • How about lowering it to 5.8? 🙂 Remember that 7.0 is neutral, so 6.8 is barely… acidic, and would have little effect on scale. Most test kits won’t test to 5.8, so you have to do the math, to figure out closely how much acid that would take, to lower your pH to 5.8, and how much base will need to be added after the procedure, to raise pH and alkalinity again.

  9. We are getting our above ground pool opened up for the year. We’ve had a terrible calcium buildup the last 2-3 years, and it looks like it’s flaking off on the bottom of our vinyl liner in a few spots. What can we use to break up the rest of the calcium on the liner without draining the pool? Would that be possible, or should we just invest in a new liner and start over? The liner itself is about 7 years old.

    • Hi Irene, you could use pH decreaser, broadcast over the pool, to drop the pH level to a 6.8 or so, and lower on the surface, as it dissolves. Let it sit for a few minutes, and then brush around gently. But first do a test run, to see if it is effective, in a small area, with a cup of pH decreaser. Note that this is not normally recommended for liners, to dump dry acid on the surface, but this scale calls for strong measures 🙂 Another method that may work is to get a bottle of Scale Free, and follow the label, and see if you can, with a low pH level assisting, dissolve and absorb the calcium into solution.

  10. Grey gunnite pool was not cared for over seven months and got very green and muddy. Pool was drained, and some parts can be cleaned ok with a pressure washer, but some have a hard white build-up that will not come off with pressure washing. Water was very hard. Is this old dead algae that has crusted onto the pool walls and floor, or calcium deposits? Is acid washing my cure either way? The sandstone rocks of the waterfall have the same white crust. Do I clean that the same way?

    • Hi Randy, yes acid washing, but first using scraper tools to knock off most of the scale, then a 50/50 mixture poured with a flower watering can, scrubbed briefly with stiff brush on a pole, then hosed completely within 60 secs. Repeat if needed, but be gentle as it degrades a plaster surface as well as the scale. Pool should be wet first, and be careful that the acid mix does not flow from shallow to deep end in one thin channel, spread it out, so it won’t wear a groove from shallow to deep. You can hire this task out, but if you choose to do it yourself, please be careful with fumes, you can use a mask for acid fumes. Goggles and gloves also good to use. Always have two people, one pouring, one hosing – go slow, section by section, pour the deep end ‘bowl’ first, then walls all around, then shallow end floor to deep. Neutralize before pumping out waste water. The pool deposits sounds like calcium scale, same with rock wall, but that’s a bit different, we call it efflorescence, originating from within.

  11. Is it possible to use a standard pressure washer to remove calcium from the pool tile?

    • Hi Rob, good question – yes it is possible, however (!) any loose tile may be loosened further, and bits of grout may be blown out, but if one was careful, and the pressure washer not too powerful (<1500 psi) it could be done successfully, without damage to tile or grout, if one was very careful…

  12. Stephen Patterson

    Is there a grout sealer product that can make the pool side tile grout water proof. Pool water is permeating through the grout and getting into the back of the zero edge wall and popping the wall tiles loose ? Thanks

    • Sure Stephen, there are a number of sealers that can be applied to the tile, or painted onto the grout, grout sealers. You can find at any home/hardware store.

  13. Hello. I have a brand new pool that was built back in December. This pool has a dark plaster and is now completely covered with scale even in the bottom. The pool is only 6,800 gal. I was told by the builder that I shouldn’t drain the pool because that will void the warranty. How can I remove the scaling without draining the pool?
    Thanks!

    • Hi Kelvin, draining and acid washing would be the fastest way to remove the scale. Another less effective way is to plug the plumbing, remove the light, and add enough acid to the pool to drop the alkalinity to near zero (about 1.25 gals), which will dissolve most or all of the scale, then use a sequestering agent (Stain Away, Scale Free), to keep the minerals in solution. Not a very uncommon problem actually, for dark plaster pools to show scale and discolorations. And I hate to tell you, but can come back again if the sequestering agent level dips, or for other reasons, like hard tap water, or shocking with calcium hypo. So you might try to get used to it, a little bit :-). We wrote a post recently about draining a pool safely.

  14. JR Rajan

    Ionized water, which produces alkaline water in pH of 8.5 – 9.5 leaves such scaling in the water bottles.
    Is it safe to consume those?
    Is there a way to get rid of it, or is it a by-product of wanting a high pH of water for drinking?

    • Hi JR, high pH does create a scaling condition in the water, making it easier for water to precipitate minerals which deposit as scale deposits or crystals in some cases. Assuming that the scale is calcium or similar mineral, I would think it safe to drink as such minerals are good for ya!

  15. Olivia Carey

    We live in Arizona. We plan to cover our pool this winter, turn off the pump, and stop the maintenance. We did last winter, but didn’t get it on until January – no problems. The primary goal is to stop evaporation and lower our water and power usage.
    So I just got this message in my pool maintenance statement, “If you use a cover, remember to uncover the pool for at least a half day each week. Tightly covering the pool for extended periods of time promotes calcium scaling.”
    That seems counter-intuitive to me. Wouldn’t preventing evaporation reduce scaling?

    • Hi Olivia, very interesting. I applaud your idea to do what I call a ‘sunbelt pool winterization‘, something we’ve blogged about before. I don’t believe that a pool needs to ‘gas-off’ as a method to control calcium scaling, I did some searching on it, and found no quick source on the question, so I don’t believe it’s a concern. More of a concern to prevent calcium scale during winter is that the pH and alkalinity levels be maintained. Scaling is less of an issue when the water is colder too. I don’t think you have anything to worry about. Good question, thanks!

  16. karen boltax

    will adding a filtration/softening system to my house (that removes the calcium) correct this problem?

    • Hi Karen, indeed it can – if you fill the pool from water that has gone thru the home water softener, or over a few years, use only treated water as make-up water, it will lower pool hardness levels and total dissolved solids, too. However, most outside spigots and pool auto-fills are often not connected to the water softening units, which is usually reserved for laundry, kitchen and bath water, so you would have to make a connection to water – usually there is a spigot somewhere near the tanks that you can connect a garden hose, or you can have a plumber add a new line to the pool area, or to the auto-fill, if you have one.

  17. Kent Kaughman

    I have an in-ground lined pool where I am having problems with excessive pressure on the filter. The filter is a couple of months old an is clean. I pulled the filter out and ran the pool pump circulating water back the the pool. The pressure with no filter is 15 psi and seems high to me. I have only owned this property for a short period of time but I am expecting their is a scale buildup in the return piping back to the pool. An ideas how to remove the scale from the piping?

    • Hi Kent, scale buildup in the pipes is not normally a problem with PVC plumbing, and if it was, you could see it at the bottom of the skimmer, or in other visible areas of the plumbing. It is possible that the return pipes could be clogged with something else however, leaves, rocks, broken check valve parts, golf balls even. Also possible that the filter is just too small for the pump size. Every filter has a ‘design flow rate’ on the label, make sure your pump is not capable of higher flow rates (by consulting the pump curve for you particular make/model pool pump). Also possible that the filter gauge is faulty, does it go all the way to zero, and is not stuck? With higher pressure on the filter, you would also expect to see lower than normal flow. 15 psi without a filter is high… every system is different, but ideal or average is usually closer to 8-10 psi clean, 15-17 psi dirty. Or 2-3 psi without the filter cartridge or grids inside the tank. So yes something may be wrong, but likely not scale, I don’t know of any remover anyway. You can scope pipes out now pretty easily, cheap scope cameras that attach to your phone camera…

  18. Roger Langille

    Several calcium deposits on bottom of pool. I do not want to drain. Poo guy recommended a putty scraper and then machinist sandpaper. I was going to buy a putty knife that attaches to a pole, but lost on machinist sandpaper in a full pool. Any ideas

    • Hi Roger, putty knife is a good idea, not too big, unless the scale is really soft, first dull the edges to prevent gouging, which you may do anyway, if using it on a pole 😉 – best to be in the pool, underwater with weights! 🙂 Pumice stones and PoolStones can also be used, as well as volcanic scrubbing rocks, aka sanding blocks. All can be used underwater. If you drain the pool, it can be sanded with belt sanders and then acid washed lightly to finish it. But in cases where you can’t drain, you can scrape it off. Might be helpful to also go under continuous treatment with a Stain & Scale chemical (immediately) like Stain Away or ScaleFree to control the calcium, and keep the pH level always below 7.8.

  19. Len Marino

    Davy, our last names are similar. you mentioned high pressure beads as a pressure wash to remove the thick calcium buildups. I don’t like working with acid personally. When I add it to the pool to adjust ph it always create a cloud of toxic vapor. So I think I may hire a professional to remove the calcium from the tile surrounding my pool and on the sides of our hot tub that empties into the pool. What happens with those beads, do they drop to the bottom of the pool and get picked up by the polaris and then disposed of or does the vendor normally clean them up.

    • Davy Merino

      Hi Len, yes very similar! Our ancestors must have been sailors or ‘mariners’. The beads are normally vacuumed up by the vendor. Some may remain or some ricochets may be found in bushes, etc later. The polaris will get any remaining, or the main drain. Bead blasting systems or portable abrasive blasters are affordable at $150+, and connect to any air compressor. Fill the blaster tank with glass or ceramic beads ($25), and you could do it yourself! Maybe you have some neighbors that will split the cost with you ~

  20. Hi!
    Good thread going here. What about fiberglass pools? I have a dark blue pool which is now completely white. Acid washing and other chemicals have not worked. I sanded a spot with 400 sand paper and it looks like new Where I sanded.
    How can I tell if it’s calcium or just faded?

    • Hi Melissa, if you had microscopic eyes, you could tell by looking at it, or if thick enough you could ‘feel’ the calcium deposit. Pretty tough job to sand the whole pool, but it’s been done before… you could hire a couple of laborers to do it for you, with some careful instruction first. Use sanding blocks or vibrating electric sanders perhaps, but not orbital sanders.

  21. Hello,
    I have scale on the tile of the water line of my pool. Is there anything I can do w/o draining water??? I live in Texas and it is hot and we use a ton of water anyway, just hate to drain a lot of water to get the water completely off the tile.

    • Hi Paige, you can scrub the scale with a pumice stone or poolstone block, without lowering the water. Or if you did lower the water to the bottom of the tile, you could use an acid mixture to dissolve it, but is ineffective on thick scale, first one usually scrapes off the majority of it with a putty knife or something dull and strong. There are companies that will bead-blast pool tiles to remove calcium scale and efflorescence, but I’m sure they lower the water first.

  22. Ron Wittman

    Hi. We have an older concrewte painted pool and when we opened this year, there is blavk looking scale formed in patches all over. I thought the paint was chipping and we kept having algae form on the sides. Took water samples to our pool supplier an got the water balance perfect. Algae kept coming back and we decided it was the sand filter and changed the sand. Now we have crystal clear water and still the black stuff. Can scrape it off but is really tough to clean off. Chewmicals? that might disolve it off?

    • Hi Ron, sounds like it could be the dreaded black algae, which responds only to very high levels of chlorine, sustained hyperchlorination – over 30 ppm for several hours. Even that won’t help sometimes, and the pool needs to be drained, pressure washed, acid washed, rinsed and pumped out, and then bleach washed. And then give it a new coat of paint.

  23. Had my pool re-plastered last year and it looked good. Covered it for winter, maintained water balance and circulation. Some dirt and leaves did get in pool. When uncovered water looked OK but dirt would not sweep up or vacuum. Dirt on steps and walls looks like it should just brush off but will not. Tried a stone on it and it did smooth some of the roughness but dirt remains. Water is balanced and looks good but pool steps and sides look bad. Tile and waterline look good.

    • Glen, sounds like a mixture of calcium scale and other gunk – which can often happen with new pools with the combination of high calcium hardness and high pH. The best treatment is to lower the water level to the floor and acid wash the walls and steps, then refill the pool. If that is too dramatic or hard to accomplish, you can try using a scale agent like Scale Free, which may (might) remove the scale, or some of it.

  24. Paul Dalton

    We have mesh safety cover that we place over the pool in the winter.

    This past winter, it developed a number of white “stains”, which we assume to be calcium deposits. We rinsed, then – while wet – scrubbed the cover with a brush. Some of it came off, but a lot remained. Next we tried applying ‘cleaning vinegar’ directly on the remaining “stains”, again scrubbing it in, letting it sit for a bit, then rinsing it all off. It seemed to help a bit more, but many of the “stain”s still remain. Next, we thought about trying CLR or LimeAway (each of which claims to remove calcium deposits), but the bottles for each said not to use the product on fabrics, so we didn’t.

    Can you recommend anything else we can try to remove these calcium deposits from this mesh pool cover?

    • Hi Paul, that’s a new one for me, removing scale from mesh safety cover – I would think Vinegar would be a good choice, but CLR and Limeaway… I see your concern, you don’t want to burn a hole right through the cover! However, I think you could test a small spot and rinse off within seconds. You can also dilute it at first, to see if half-strength will work. Or you could just learn to love the abstract art created by nature, and the science behind it… 🙂

  25. I have a hot springs vista hot tub and i was sold the chlorine for pools instead of tubs. Now there is crystalline build up all around where water was and it feels like sand paper. Is it safe to use and will it work muriatic acid to spray the surface once drained and if yes what would be ratio water/acid or do you have any other suggestions to get rid of that and restore smooth surface back to original ?
    Thank you.

    • Hi, sounds like calcium deposits, very likely if you have high calcium hardness levels in the water, and a high pH at the same time. Lowering the pH to 7.2 may allow you to brush off the deposits, try that first. If that doesn’t work, lower the water level and try a pressure washer on the deposits (carefully) – if that doesn’t work, yes you could use an acid solution – but maybe start with Vinegar, much milder than muriatic acid. IF that doesn’t work, a 50/50 blend of water/acid could be used in a (clean) spray bottle (carefully). Let it soak for 45 seconds and rinse it off (test a small area first, but your acrylic tub should take it, although some of the sheen may dissolve…?) Not sure actually, never tried to acid wash a portable spa….

  26. I have drained my pool to prepare for acid washing. I’m concerned that too much acid will damage my plaster. However, I have a lot of scale build up on walls, steps, seats, and turtle shelves. What is a good mix of acid and water that will be effective and non destructive to the plaster?

    • Davy Merino

      Hi John, start with a 50/50 mix, always adding acid to water (not water to acid). Use a flower watering can to pour the acid over the surface, working small areas at a time. If 50/50 works really well, you could dilute the solution to a weaker mix. If it does not remove the scale, you can hit it again, or increase the strength. Experimentation on your particular pool stains can help determine the correct mix that will remove the stains, (but not the plaster). Hang time is also an important consideration. Rinse off quickly, within 30-45 seconds, or sooner if you can. The longer it is on the surface, before rinsing, the more chance it has to etch the plaster. Rinse completely, and rinse the floor while it runs into the deep end, to prevent wearing a channel down the center of the floor. And one more tip – be sure the surfaces are moist, or wetted down, before pouring on the acid.

  27. We just had our salt water pool resurfaced back in August 2017 and we have a layer of calcium build up alover the pool and some larger clumps of it as well. Had water tested and it’s so high it doesn’t even register. What can we do to remove with out draining our pool since it is in ground and if not done correctly can pop outta the ground… Can we and will it even help put a few gallons of acid in and brush walls?

    • Davy Merino

      Hi John, don’t worry about the pool popping – unless you have been warned by your builder never to drain it – you could drain half, and refill if you don’t want to do the whole thing. Most pools are in no danger of popping, only those that sit in a topographically depressed area with a high water table and expansive soils, and a 100-yr storm event or hurricane type flooding. Doesn’t happen often. Even when hydrostatic relief valves are not opened… So yes, the best solution to calcium nodules or crystalline deposits is to drain and acid wash or sand with a belt sander. You could just use a pumice stone or sanding block, underwater, and get it all done, while you exercise! Adding acid and brushing may help, but probably not much. Using a product like Scale Free is a good idea to keep minerals like Calcium locked in solution with chemical bonds.

  28. What about pebble finish and stones? Shall I use pressure washer? Will PoolStone even work or it will be gone in no time against this type of surface?

    Thanks!

    • Davy Merino

      Good question Vitaliy, rougher surfaces do deplete the PoolStone and Pumice stones more than a smooth surface. A pressure washer is a good option, but if too powerful it could damage the grout in between stones and tiles, but under 2000 psi, with a small tip and some precision, you can get most scale removed. Then use a weak acid solution to clean up left over bits and haze.

  29. Hi, I have a medium sized indoorpool. The water has turned milky in colour and the calcium is high. Is there a way to remove it from the water?

    • Davy Merino

      Hi Richard, there is no easy way, no chemical or process that will reliably remove calcium from the water, with exception to high efficiency filtration or water softening systems. I wish we had an easy ‘calcium reducer’ chemical – a few have come and gone over the years, but nothing has really worked – the solution is dilution. However, you can control calcium scale and cloudy water if you use a Stain & Scale chemical like Stain Away or Scale Free, to keep minerals locked in solution, where they can’t come out, to cloud the water. Doesn’t lower the calcium level, just keeps the mineral dissolved. When calcium is high, and it comes out of solution, a nice big filter can trap a lot of calcium. Sand filters can use a cup of Aluminum Sulfate to improve filtration. You can use pool clarifiers (but don’t overdose) to assist a small filter, during a clouding event. Cloudy water can come from calcium, but can also be an indication of poor filtration, not enough filtration, or low chlorine levels, all of which can make the water cloudy.

  30. Hi. I have a new pool and spa with glass tiles around the inner edge. Already, there is lots of calcium that looks to be dripping down from the bottom of the coping. My pool guy said to use a pumice block, but that seems way too abrasive for the glass tiles. What do you recommend?

    • Davy Merino

      Hi, calcium from the coping can be acid washed off, after scraping off the big stuff with a screwdriver, putty knife, wire brush or yes, pumice stone. Test a small area first, but most glass tiles are more scratch resistant than you may think. To slow the efflorescence, consider sealing the coping stone and mortar bed above the wall, with a clear concrete sealer. Reapply every year or two. You can also seal the glass tile, to reduce the bonding of the calcium, making it harder for it to stick.

  31. Rockwell

    we have a tile pool with a very heavy calciumdeposit on it. We have tried to clean with muriatic Acid but doesn’t seem to work. Could with use a sander with a finer sand paper so off it then muriatic once again?

    • Davy Merino

      Hi, for rough efflorescence I usually scrape it off first with a small putty knife or large flathead screwdriver. Sanding may work, but it is usually kind of wet, so it may gum up quick. You can scrape pretty hard on most pool tile without damage to it, so you can get most 90% or so, off manually, and then hit it with acid to finish, maybe twice. A plastic or soft steel rotary wheel on a (cordless) power drill would also work fairly well.

  32. Niall Parker

    If a pool is in a hard water area and using Calcium hypochlorite, ideally it should change to sodium hypo but in the interim I have heard adding salt tablets to the skimmers can reduce scaling and calcium build up. Is this true

    • Davy Merino

      Hi, I’ve not heard that before, and my thought is that it would not be true. Using a sequestering agent will help control scale, but calcium will still rise. You can also use Di-Chlor pool shock, or non-chlorine pool shock, to stop adding additional calcium to the pool, from Cal Hypo.

  33. i have bad hard water calcium on the tile above the water line. Tried muriatic acid and it didn’t do much. Tried pumice stone, and its too much work. Will renting a pressure washer with 2000+psi work to remove it? its pretty thick calcium. Rather not pay $$$ for professinal to come bead or soda wash….

    • Davy Merino

      hI Monty, yes you could use a pressure washer, however, if the tile or grout is loose, it could cause some damage, so be careful. Standing in the pool will be more precise than standing on deck, I suppose. Putty knives or screwdrivers are also good to pop off calcium scale. Acid wont do much for thick deposits, but is good for thin films. Muriatic acid in a spray bottle is my method. Often takes 2-3 treatments. pH will drop of course, use 1-2 lbs of ph increaser for each gallon of acid used, to raise pH again. So yes, the pressure washer will work, but go easy, just get the big stuff, then finish up with some acid to remove the filmy scale left behind, as needed.

  34. G. Campbell

    I have a above ground 15,000 gal. vinyl liner. This year I starting using aqua silk chemicals. (Last year I used softswim from the pool store)
    Test strip readings
    PH : 7.2
    Alk: between 40-80
    Biguanide: between 30-50
    Total Hardness: 0

    My question is what level should the total hardness be? The water stays slightly cloudy. Can I use any brand of calcium raiser with aqua silk?

    Thank you for the help

    • Hi, it might be unlikely that your total hardness level is zero. The recommended level is 200-400 ppm, and yes you can use any brand of calcium hardness increaser with biguanides.

  35. I have stainless pool walls. It looks like I have scale build up below the surface line. I could not see it when it was full. I emptied the pool to paint and it extends to the bottom of the panels. Any idea how to remove without acid?

  36. Rose Lauck

    What about a vinyl pool. I have learned about calcium scaling way too late and now have a swimming pool with tons and tons of calcium deposits all over the liner particularly in places where there are divots? What are your step by step recommendations?

    • Hi Rose, great question, we seem to have forgotten to discuss vinyl. Sounds like you may have crystalline deposits? First thing is to balance the pH and alkalinity. Test and adjust pH to 7.2 or so, and alkalinity between 80-100 ppm. keep a good chlorine level and start running the pump and filter a bit longer than usual. Add a good sequestering agent, (a stain & scale) like Stain Away, or Scale Free, to lock up the minerals, back into solution. Brush the pool daily, buy a new brush if yours is old and small, to help loosen the nodules. Check pH daily, and make sure it stays low in the 7.1-7.3 range. If no improvement after 3-4 days, you can carefully take the pH a little lower, into the more acidic 6.8+ range, but only for a day or two, while brushing, to help dissolve. Then raise pH again to 7.2-7.4, and adjust alkalinity again if needed, to 80-100 ppm.

  37. Does efflorescence occur on tiles that are below the water line i.e. does it require some interaction with air to occur?

    Aesthetically, we’d prefer to line our pool with stone pool tiles (rather than glass mosaics), but are concerned that even if we pre seal them, they will be affected by efflorescence.

    • Davy Merino

      Hi, efflorescence occurs from the rocks leaching the minerals from the backside of the pool, into the pool, and moisture on the front side accelerates it. This does occur when stone mortar is below water level, but it just dissolves into the pool, so you never see the stalactite-like remains, as you do above water level.

      The best way to prevent efflorescence is to seal not just the front side, but the back side. Prevent ground water and pool water from getting behind the wall. if there is a deck over top of the raised wall, that will stop much of the water, but not all. Sealants or membranes (rubber layers) can be used on the outside of the wall to keep the wall dry, along with effective de-watering design, (gravel and pipes and underground swales), to channel water away from the area.

  38. Our pool was built in 1972. It has fiberglass walls and concrete floor. Can I use something like car (Turtle) wax on the walls to remove the oxidation and restore the color?

    • Hi Jacen

      Yes, you could use any fiberglass auto/boat restore product, or rubbing compound, and a coat of wax sure. I don’t think you’ll get too much color back, but it wouldn’t hurt. Test a small area and see how it does! You could also sand it and paint with epoxy pool paint ($$), or you could even tile the top foot of the walls ($$$), which looks really sharp. Or, there may be some mobile gelcoat or fiberglass resurfacing companies in your area that can apply a new gelcoat ($$$$). But these are just fanciful ideas. There may be a sort of product that can ‘stain’ the surface, but I’m not aware of one.

  39. I had no idea that there are chemicals that are useful for calcium buildup removal. I also had no idea that you could use pressurized sprayers to more effectively remove calcium buildup. I’ve heard it’s a good idea to do pool cleaning and maintenance weekly, I’ll have to look more into it though.

Comments are closed.