The Ultimate Guide to Pool Water Balance

pool-water-balance--It really is a balancing act – to maintain the correct levels in the pool water. If pH or Alkalinity is too low, or Calcium Hardness levels are too high, there can be problems.

Other pool chemicals also must be balanced and in a certain “safe area” – an ideal range for each component of water balance that is tested.

Pool water quality is affected by the level of pH, which is affected by Alkalinity. Pool water pH levels that are too high can cloud the water or create scaly deposits, but low pH levels allow for pool equipment and surfaces to become etched and corroded.

Adding too much chlorine can cause skin and eye irritation. On the other hand, when levels of sanitizers are too low in a pool, they will not provide the power to kill algae, bacteria or other contaminants.

Water Balancing chemicals are important because they prevent damage to the pool, or poor sanitation from chemical levels that are too high or too low.

Chemistry of Water Balancing Chemicals

Water balance for pools essentially means to bring into balance, the most important being the pool pH, Total Alkalinity and Calcium Hardness levels.

POOL-WATER-BALANCE-PHpH measures the acidity or basicity of the water. The pH scale goes from 0 to 14, and 7 is considered neutral. Anything under 7 is acidic, while anything above 7 is considered basic. Pool pH of around 7.4 is best.

Pool water pH values below 7.0 creates a corrosive environment, or an acidic condition. Add a base to bring the pH up, into a more basic range to prevent corrosion.

pH levels in the pool water have ideal range of 7.4 to 7.6, and whether higher or lower, it’s not good for the pool or swimmers. At levels above 7.8 only 50% of your chlorine will be active.

Pool pH that is above 7.8 creates a scaling or basic condition. This means that scaly deposits may form, or cloudy water problems. High pH also reduces chlorine potency. Add an acid to bring down the pH to prevent the formation and build-up of scale.

pool-water-balance-taTotal Alkalinity measures the hydroxides, carbonates and alkaline substances in the pool water. A close cousin of pH, Alkalinity buffers your pH, keeping it more stable. When TA is too low, pH levels are erratic, and not stable.

Raise low alkalinity by adding a base to the pool, specifically products labeled Alkalinity Increaser. TA levels should be 80-120 ppm. Total Alkalinity strongly influences your pH level, so if your pH is off, be sure to check the alkalinity.

Lowering Total Alkalinity by adding an acid to the pool water. This is harder than it sounds, because it also lowers pH levels when you add acid. Certain types of acid will lower Alkalinity more than pH, but it can still be a process of lowering TA, raising pH, lowering TA, raising pH…

POOL-WATER-BALANCE-CHCalcium Hardness measures the softness or hardness of the water. Hard water has higher calcium or magnesium content. These particles can deposit themselves on pool surfaces, lights and ladders, or can frequently come out of solution making the water cloudy.

Calcium Hardness is another important factor to any pool. Water can get murky and scale formations can occur as well as stains. It is important to keep calcium hardness levels below 400 ppm, but the most desirable range is usually 180-220 ppm.

When calcium hardness is too low, add Calcium Increaser. The water is then too soft and can corrode surfaces in the pool. If levels are too high, scale deposits and cloudy water can become a problem.

What’s Temperature got to do with It?

ducky-pool-thermometerThe Langelier Saturation Index can be calculated by testing water for pH, total alkalinity, calcium hardness, cyanuric acid and, temperature. When water warms, from 70° into the high 80’s – this changes the way water balance components interact.

Generally speaking, higher water temperatures makes your water more active, and is balanced at lower levels for TA, CH and pH. When water temperatures are cooler, higher levels are recommended.

The Saturation Index uses a temperature factor to tell you the ideal levels for TA, CH, Cya and pH. The math is a bit complicated, and involves charts, but Pentair has an easy to use online Saturation Index Calculator.

Other Pool Chemical Levels

Full analysis would include testing for Total Chlorine and Free Chlorine levels, and for Cyanuric Acid levels in the pool.

POOL-WATER-BALANCE-CLFree Chlorine is the amount of chlorine that is available to work with, not including Combined Chlorine, or chloramines. When you test your water with a DPD test kit, you can test for Free Chlorine (FC) and Total Chlorine (TC).

Subtract FC from TC, and you get CC, or combined chlorine. When CC is over 0.3 ppm, it’s time to shock the pool to remove these contaminants. Free chlorine levels should be at least 1.0 ppm.

POOL-WATER-BALANCE-CYACyanuric Acid retains the chlorine in the water for a longer period of time. Stabilizer is added to some chlorine to protect from breaking down – which occurs from UV rays. When the pool stabilizer levels are low, your chlorine won’t last as long.

The ideal range is 30-50 ppm, and better on the low end as new research suggests that high levels of Cya can suppress chlorine activity and potency.

POOL-WATER-BALANCE-TDSTotal Dissolved Solids is another important factor to pool water balance, although it is not often tested unless pool water conditions have become unmanageable. When water evaporates, minerals are left behind – and as evaporation continues, the water becomes more saturated, which makes it harder for chemicals to be successful in their endeavors. This in turn gives pool stains an opportunity to come out and appear in the pool.

The only way to lower TDS is to drain some water out and add fresh water. Recommended levels for TDS are less than 2000 ppm, or 5000 ppm for pools using salt chlorinators.


  • Test 2-3x per week, adding adjustment chemicals as needed.
  • Run the pump after adding chemicals, to help distribute.
  • Add one chemical at a time, or add them into different areas.
  • Test and adjust in order. First alkalinity, then pH, then calcium.
  • Use the Saturation Index to consider water Temperature.

taylor-dpd-cl-brPool chemical levels can be crucial to the health of swimmers, as well as the health of the pool. Unsanitary water, stains and corrosion are common in pools with consistently unbalanced pool water.

To avoid these problems, test and balance your pool water regularly, and enjoy your pool with less mess, and less stress!

Alex Malamos
InTheSwim Staff Blogger


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The Ultimate Guide to Pool Water Balance — 44 Comments

  1. I have an 18′ X 48″ salt water pool that became overrun with algae when I was away. I have gotten it under control but now can’t clear the water up or get the balance right again. Right now my levels are as follows: Hardness, 500, Chlorine, 0, Free Chlorine, 0, Ph, 7.8, TA, 240, and Stabilizer, 0. The pool water is very warm, probably around 100 degrees f. As recently as a week ago everything was pretty close to good except for free chlorine levels, which were low. There are frequently a lot of people using the pool and I live in Mesa Arizona so it is always in direct sunlight. How can I maintain the correct levels of everything in my pool. I also need to add 2 more 40lb bags of salt.

    • Hi Jeannie, sorry to hear of these troubles. OK, first thing I would do is drain half the water and refill the pool, to get cleaner water with less hardness and alkalinity, if possible. If not possible or desirable (Hi, Arizona), then I would first attack Alkalinity and pH by adding pH decreaser repeatedly, over several days, and up to a week of adjustments, to get pH around 7.3 and Alkalinity down to 100 ppm, or as close as you can get it. Concurrently with the pH/alk process, shock the pool with enough liquid or granular pool shock to turn the water blue-ish, and then add a little more. Also should add 2 lbs of stabilizer (Cyanuric acid) per 10000 gallons, to protect chlorine from the sun. Keep hitting the pH, because a high pH level will make the chlorine sluggish and less effective. Check pH, alkalinity and chlorine every day and make adjustments as needed. Also, start running the filter 24/7 if you aren’t already, (it won’t blow up), and backwash as needed. When the water finally starts to clear, brush and vacuum, and then you can add an algaecide, if you want to have some preventative measures in place – but to clear a green pool you don’t need algaecide, it’s all about low pH, high chlorine and good filtration. And in your case, you need to lower the Alkalinity, in order to get your pH stable, where it won’t rise quickly again.

  2. Hi … I have a 10×30 pool and I am getting the following reading with my test strips.

    FCl 0
    Alk 80-120 ok
    pH 9.0 high

    There is a chlorine tablet in the pool. How can I lower the pH and bring up the free chlorine levels?

    Thank you so much.

    • Hi, pH is too high for the chlorine to work, it needs to be 7.2-7.4 for best results, as chlorine becomes very sluggish and impotent at pH levels over 8.0 – use pH decreaser to lower the pH level, and then you should start to see a chlorine residual with your test kit. You may want to shock the pool with granular chlorine, immediately after lowering the pH, to prevent algae and hazy water, and to raise chlorine level fast, then tablet(s) can be used to maintain. Use if you want to know exactly how much pH decreaser to use, it’s not much – in a pool so small, maybe 1 cup and then retest.

  3. Hello Guys, I’m new to pools we recently installed a 45,000 Liter Fiberglass pool. I’m having a hard time grasping the pool balancing act. I have a Astral EQ25 that automatically detects both Chlorine Levels and pH. Finally happy with the pools after changing some of the settings. Had my water tested the other day.
    Total Chlorine 1.0 (Its winter over here so no one is using it)
    pH 7.4
    Hardness 158
    Alkalinity 38

    So I purchased some Alkalinity Increaser and now ph is 8.4 after adding kgs in a bucket and mixing with water while adding onto pool.

    Seems to be a viscous cycle, any help would be appreciated.
    EQ25 has Salt Chlorinator Cell and Self Dosing Acid with probes.

    Thank you in advance.

    • Making big changes to Alkalinity is a bit of a viscous cycle, yes. But it will end, after a few cycles of raising Alk up, then lowering pH, raising Alk up, lowering pH again… until you get it right. When adding the pH decreaser, broadcast it, or pour it widely around the edge, instead of adding it all in one spot. This is supposed to have less effect on alkalinity. Because, as you know, when you add the pH decreaser to lower pH, it will also lower the Alk somewhat. Keep at it, you’ll get there. The self dosing acid may causing the problem, perhaps a probe sensor is dirty, or is causing the problem in some other way, constantly lowering your pH, which hammers your alkalinity as well…

  4. We’ve had a lot rain lately and my pool is cloudy, greenish color. I’ve vacuumed it and added chlorine tablets, algae liquid, shocked it, still not clear.
    Readings are:
    0- free chlorine
    Ph- 8.4
    Total alkalinity- 240

    • Hi Krista, first thing to do is get the pH/Alk down and the chlorine up, right away or things will get worse. Add 2 cups of acid, or a pound of dry acid to the pool, per 5000 gallons, to move from 8.4 to 7.4. Your test kit may not go beyond 8.4, so it may actually be higher, and the high alkalinity will resist changes to the pH, so you may have to treat several times to see a solid effect to get pH down around 7.4 and alkalinity down below 150 ppm. In the meantime, add more tablets and more shock chlorine to keep some sanitation going on, and once the pH and alkalinity are lower and stable, shock it hard with 2-3 lbs of shock, per 10000 gallons. Run the filter 24/7 until resolved, it’s hot out!

  5. Hi i tested my 20X12 semi-inground SWG pool usingColorQ pro-7 and got the following readings
    FC 7.87
    TFC 8.79
    PH 7.4
    ALY 107
    CH 89
    CYA 60
    salt 3400 PPM
    question my water is starting to give off a strong chlorine odor is this ok or am i doing something wrong? BTW the temp was at 80 degrees and the water is perfectly clear.

    • Hi Naz, the difference between total and free chlorine is enough to warrant a good shocking – from your first two results, (TC-FC=CC), you would have a good reason to shock the pool. they say, to shock the pool when the the difference is 0.3-0.5 ppm – between total and free, basically if the sample darkens at all, that indicates the presence of chloramines, and you vnearly 1.0 (0.92) ppm of chloramines. Shock the pool to 10-15 ppm, using 2lbs of pool shock, per 10K gals. That should take care of the smell, and destroy the chloramines, which should be shocked to 10x – 15x the chloramine level, for effective and complete removal.

      • Thanks for the quick reply… can you recommend a good shock to use? oh and one more question i’m using Hayward AQ-TROL-RJ and it’s set to 60 ppm do think i should raise it?

        • Hi again, Cal hypo shock would be good choice. You mean it’s set to 6.0 ppm (not 60) I suppose, I would lower it to the 3-4 ppm range, no need for the extra chlorine, it just makes the salt cell work harder, and idle chlorine more readily turns into chloramines…

  6. Trying to get my chlorine levels up. After shocking twice and keeping 2 tablets going – level is still 0. Other readings are PH 7.8, TA 180, TH 400, CYA 70. From reading your article looks like my TH and CYA are off. Would that cause the chlorine to be 0? If so, how can I get the chlorine level up? My pool is 15′ round, 4 foot deep. Thank you so much for your help!!

    • Hi Trudy, try a double or triple dose shocking, try 2 lbs of shock. An unrelated problem could be the high pH/Alkalinty, not so much hardness and cyanuric actually which normally is good up to 100 ppm, or even a little more. First, I would lower the Alkalinity, which will take several attempts. Add 2 lbs of pH decreaser to your 5K gal pool, to drop pH level to 7.0. Pour the dry acid into a bucket of water, and then pour into the pool, in one spot, with the pump off for 10 minutes. Turn the pump back on for a few hours. Then raise the pH back up again by adding 2 lbs of pH increaser, directly to the pool, broadcasting over the surface or pouring along the edge, with the pump running. Repeat the process again after a few hours of circulation, and brushing the pool. Then test alkalinity and pH again. Repeat again as needed, over several days sometimes, to bring the Alkalinity down to around 100 ppm, which will then allow you to adjust the pH level to a more chlorine friendly 7.4.

  7. Hello,
    I have a 2,750 gallon above ground pool with a PH above or at 8.2. I’ve been adding dry acid but the PH won’t go down. My Alkalinity is 110ppm and my CL Br is like 0. My pool went from green to cloudy, bought a new filter and nothing. I’m very confused as to what steps to take.

    • alkalinity of 110 ppm is not too high, so it shouldn’t prevent pH adjustment, but may take a few tries. For your size pool, to go from 8.2 to 7.4 should take about 7 oz. of dry acid or 5 oz of liquid, a very small amount in any case. Very high chlorine would / could give a false high pH test, and when tested, the sample may bleach out, first showing color, then turning clear within seconds – if that is happening, it could be interfering with the pH test, making it appear falsely high. But since you say you have no chlorine in the water, then… try again on the pH decreaser. Your pH may be actually 9.2, but it can be hard to tell what it is when it goes off the scale…

  8. Chlorine 3/6
    PH 8.4
    Total alkalinity 240
    Total Hardiness 100
    Cyanuric acid 100

    Water is a bit cloudy and ambient temp is 100F. Since acid is already too high, how do I get the water back in check? Pool was emptied and refilled about a month ago.

    • Wow, that’s messy! First drop the pH and alkalinity into range, by adding several gallons (depending on pool size) of muriatic acid or pH decreaser. Add the pH down with the pump off, and pour it under-water (not splashing along the surface, but gently underwater). It may take several treatments to lower the Alkalinity to 120 ppm, and then your pH will be very low, so raise it up with pH increaser, which also may take a few treatments. When pH is 7.4 and alkalinity 120 ppm, you can then adjust your calcium hardness, by adding calcium increaser, to raise it to 180 ppm. Cyanuric acid is also way too high – twice the limit. Ugh – if possible you may want to drain the pool again, is your tap water this messed up? Maybe drain half the pool, refill and try again – should be cheaper and easier than the alternative, or maybe not if your tap water tests poorly.

  9. have a 10 x 30″ pool filled up 2 days ago was told to add
    1lb of Clorox pool and spa shock xtra blue.
    just tested the water and found that my
    FCI = 10
    ALK = 0
    PH = 6.2
    Thank you for your help

    • Hi, the water is very acidic, don’t worry it won’t burn your face off – but it is not good for the vinyl liner. If Alkalinity is really zero, it will be hard to maintain pH, as alkalinity has a ‘calming effect’ on pH. You may need to also add some Sodium Bicarbonate (Baking Soda), aka Alkalinity Increaser. For your very small pool, which only has about 1200 gallons, you don’t need much. Try using the Poolcalculator, to help you determine how much of a particular chemical to add. By my calculations, you need about 1 lb of Baking Soda, and 2.5 oz of Ph Increaser. Start with the baking soda, just pour it in, and then test pH and Alkalinity after a few hours.

      • Hey there, my alkalinity and Cyanuric acid levels are both too high! Should I empty the pool half way and refill? I wanted to swim today :/

        • Hi Brandy, that would be the fastest and easiest solution, to drain half the pool and refill. Test your tap water first though, just to be sure that it’s much better than the pool water, which is probably is. Alkalinity can be lowered with an acid, but it also lowers pH, and can take weeks of see-saw adjustments sometimes. Cyanuric Acid has a new reducer product called Bio-Active, but results are mixed, does not seem to work consistently for everyone, but claims to lower cya by 50 ppm (for each $50 treatment).

  10. Hello I have a 20′ pool round by 4′ deep. I just filled it with water 2 days ago. My chlorine level is at 0, the alkalinity and ph are very high. What can I do? How safe after adding chemicals is it safe to swim. Should I add the chemicals at night?

    • Hi Maria, first get chlorine in the water right away. Tablets will take too long to dissolve, add granular shock, just 1 lb, or 1 gal. of unscented laundry bleach. Then Lower the pH and alkalinity first, by using a Dry Acid, or muriatic acid, to 120 ppm maximum alkalinity, and pH of 7.2-7.6. Dropping your pH low, will also lower the alkalinity. For your size pool (7500 gals +/-), add 1.5 oz of Dry Acid (Ph Decreaser) to the water, per 0.1 reduction in pH desired. For example, if it’s above 8.4 (off the scale), then add 10 x 1.5oz. or 15 oz (1 lb.) of pH decreaser to lower pH from 8.4 to 7.4 (10 x 0.1). If Total Alkalinity is very high, it will cause the pH to resist the change, and re-treatment with slightly larger dose(s) may be needed to see full effect Wait sveral hours between treatments, and retest the water. After confirming lower pH and Alkalinity levels, you may want to do a proper shock of the pool, with 2 lbs of shock, or 2 gallons of bleach, and immediately add chlorine tablets (3-4) to a chlorine floater or a chlorinator installed on the pipe. Test daily for chlorine and pH until you develop your system that keeps a constant and consistent 2 ppm of chlorine in the water, and a proper and steady pH level. If your pool is sunny, adding 2 lbs of stabilizer (cyanuric acid) will help protect chlorine from the sun, and lower amount used, saving money on tablets. Other Tips: Run the filter longer than you think necessary, 12-18 hrs daily, to overfilter the water, especially now (July/August) when it’s hot. Keep the pool clean, skim, brush and vacuum as needed. You may find benefit from using a clarifier to help your (possibly) small filter, and algaecide to help your chlorine, if you spot any green or yellow algae at any point during the summer.

  11. I’m confused we have a 15 x 48 round pool. Added chlorine, PH is down, put in PH increased & still not right. Vacuum everyday, missing something.Water is clear. Thank you, Lori Romano

    • Hi lori, it could be a high alkalinity that is not letting you adjust the pH level. Check the Alkalinity level to see if it is 80-120 ppm. Or maybe you just did not add enough pH increaser.

  12. New pool owner and I’m confused with the whole chemical thing. We purchased a 12×39.5 bestway hydro force above ground pool. My chemical leaves are all over the place.
    Bromine 10
    Free chlorine 3
    Total alkalinity 0
    Ph 7.2
    Total hardness 0
    I know I’m missing something..I believe it has to do with the alkalinity? How can I keep the chemicals balanced and what am I missing as of chemicals? I have only got stabilized chlorine and concentrated liquid algaecide. The water is clear but I know I’m missing something

    • Hi, if you are using chlorine, there is no need to test for bromine. And your alkalinity and hardness – can’t be zero, well I suppose it could… but not likely. alkalinity should be a minimum of 80 ppm, and calcium hardness a minimum of 180 ppm. there are increasers available for both, if you need to raise the levels. It’s possible that they need boosting, or they could be high enough already, a different test kit or strips can be used to test again. Some pools do need only chlorine and algaecide, or just chlorine and shock. You may find a clarifier useful, if your water starts to look hazy. Having shock chlorine granular on hand is also useful, if algae is spotted, or to boost low chlorine levels quickly, or after a big group has used the pool, and water looks hazy.

  13. Hi. My pool has been very cloudy you can not even see your feet. My ph is 6.7 and my alkalinity is about 60-70 ppms. The chlorine is 3-4. We changed our sand and vacuumed the hell out of it. Don’t know what to do.

    • Hi, first you should raise the pH and alkalinity, at the same time, using Alkalinity Increaser. Raise Alk to 100 ppm, then if pH is not at least 7.2, raise it with pH increaser. Secondly, add a dose of clarifier to help coagulate small particles into larger, filterable clumps. Third, run the pool filter 24/7, or nearly 24/7, until water clears. Keep the chlorine level high, 3-4 ppm is good.

    • Hi, first thing is to check the pH level and adjust it if needed, to around 7.2. Assuming that your filter is already operating, the next thing to do is to vacuum the pool to waste if possible, to remove as much material (algae/debris) as possible. Once as clean as you can get it, recheck the pH and shock it with enough pool shock to kill the algae. Generally this is about 30 ppm, but it varies according to how dark green the water is. It goes something like this:

      • Light Green: 2 lbs shock per 10,000 gallons
      • Medium Green: 4 lbs shock per 10,000 gallons
      • Dark Green: 6 lbs shock per 10,000 gallons
      • Very Dark Green (with 12″ visibility or less): 8 lbs shock per 10,000 gallons

      These are general guidelines, but basically just keep adding shock until the water turns a blue/gray color, if there is any hint of green, add more. Shock in the evening, after the sun goes down. Then brush the pool to distribute. The next morning, you should have a chlorine reading. If the chlorine level is zero, you missed the mark, and may need to shock again, to completely overpower it.

      Run the filter 24/7 until it clears, you can add clarifier when the chlorine level drops below 5 ppm. If you can drain a portion of the water easily, you may also consider draining a foot or two, and refilling, before you begin treatment.

  14. How can I get my chlorine levels. Up? 4 floating basket, 6 lbs of shock. Water is crystal clear. All other levels are on level. Chlorine registers 0.

    • If you test strips or reagents are accurate, then either the chlorine demand is higher than the amount added, or the sunshine is burning off the chlorine as it’s added because of no stabilizer, or the level of stabilizer is so high (cyanuric acid) that it becomes hard to see a reading. If cyanuric acid is a good level (not too high or too low), and you say water is crystal clear… I might suspect nitrates or phosphates, use a phosphate remover. Or sometimes there is some unknown contaminant consuming chlorine, and it just takes a hella shock (5-6 lbs per 10K gals) to break-it down.

  15. My Ph is at 6.2, my free chlorine is at 10+ and alkalinity is almost 0……….pool looks beautiful but know I have issues. Suggestions on what I should do greatly appreciated. My pool is 16×32 and 9 feet deep end 3 foot shallow end……….

    • Hi Jeff, add Alkalinity Increaser – if at zero, you need 12 lbs. per 10,000 gallons of pool water (your pool should be about 20K gallons). Then see where your pH level is, after confirming that your alkalinity is at least 80 ppm. Chlorine should drop by itself.

    • Ah, that’s a good question – start with Alkalinity, then pH, then Calcium hardness, then cyanuric acid (stabilizer) – and then adjust chlorine levels, or add any other chemicals used (algaecide, clarifers, stain & scale).

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