Bad Pool Chemical Combinations

Welcome back students of pool, take a seat for our lecture today on bad pool chemical combinations.

We will start with several water balance scenarios that can result in unfortunate “side-effects’.

Then we will turn our attention to a few pool chemicals that should always be added separately, not together.

We’ll close with a brief discussion on best chemical safety practices, to prevent accidents from oxidants.

Let’s Dive-In, shall we?

Bad Water Balance Combinations

High pH + High Calcium: A recipe for scaling and cloudy water, forms scale film on pool surfaces and pipes, and can even form sharp crystallized nodules of calcium.

High pH + Low Chlorine: Perfect conditions for cloudy water and algae. Algae prefers a high pH level, and is just waiting for a low chlorine opportunity to bloom.

Low pH + Low Alkalinity: Will cause etching and corrosion to steel, copper, rubber, vinyl and plaster surfaces. Low pH is great for chlorine potency and algae prevention, but once it drops below neutral 7.0, acidic water begins to corrode pool surfaces and equipment.

Low pH + High Alkalinity: Same as above, only it becomes hard to raise pH, due to buffering effect of a high alkalinity. Add enough Dry Acid” to lower alkalinity (and pH). Requires several doses over many days, raising pH after each treatment.

Illustration of chlorine floaterLow Chlorine + Low Stabilizer: Hazy – cloudy – green is the usual progression. If you look at your pool everyday closely, you’ll know just by looking at it when chlorine is low. Act fast with pool shock to bring the level up fast, then fill your tablet floater or chlorinator. Outdoor pools should maintain a level of stabilizer in the 20-50 ppm range.

High Chlorine + High Stabilizer: This can damage soft and shiny surfaces over years of very high chlorine levels (5-10 ppm). High stabilizer levels over 100 ppm can cause problems in chlorine potency and chlorine testing becomes unreliable.

High Combined Chlorine: Chloramines are Free chlorine molecules joined with ammonia or nitrogen. No longer an active sanitizer, they cause red eyes and smelly pools. When chloramine level exceeds 0.3 ppm (TC-FC=CC), shock the pool.

Low Calcium Hardness: Creates a corrosive water condition, causing etching, and leaching of calcium from plaster or tile grout. Low hardness is also bad for vinyl liners when the water is too soft. It hinders overall water balance and chemical effectiveness, too.

High Phosphates: Phosphates enter the pool from many sources, but when a phosphate test exceeds 300 ppb (parts per billion), reduce them with SeaKlear or PhosFree. Phosphates and nitrates are favorite foods for algae, please don’t feed the animals. 🙂

Bad Pool Chemical Combinations

cheap-pool-shockChlorine shock + Algaecide: Chlorine shock will disrupt the polymer chains or chemical compounds used in many pool algaecides, and in most cases will completely destroy the algaecide. Use pool shock to kill algae, and save your algaecide until the chlorine level has returned to normal.

Chlorine shock + Sequester Agent: Chlorine shock will also disrupt stain & scale chemicals, aka chelators or sequestering agents, if added at the same time. Add Stain & Scale chemicals a day before or several days after, shocking a pool.

Clarifier + Clarifier: If you overdose a pool with Clarifier, a curious phenomenon can occur. Instead of behaving as a coagulant, the electron charge can reverse, causing some formulas to behave as a dispersant. Wait 5-7 days to treat again with clarifier, closely following dosage instructions.

stabilizer label shownVery High Cyanuric Acid: Have I told you the one about the guy who thought he was adding calcium to his pool but actually added 15 lbs of cyanuric acid? Also labeled Stabilizer or Conditioner, when cyanuric acid levels exceed 100 ppm, proper sanitation becomes difficult. The solution is dilution.

Chlorine Shock + High Metals: How about the guy whose copper heat exchanger was eroding from low pH, who shocked his poorly balanced pool water, and ended up with black streaks and stains? High metal levels can drop-out of solution in such cases. Keep pH, Alkalinity and Calcium Hardness within range, and add a regular treatment of a sequestering agent like Stain Away or Metal Free to keep metals in solution.

The Worst Pool Chemical Combination

Never allow pool chemicals to contact each other, even a drop of algaecide, clarifier, antifreeze, or other liquids mixed with chlorine, can erupt into a raging fire. Mixing chlorine and acid (pH down) creates a deadly gas. Mixing different chlorine types can explode when moisture is added. Chemical residue from a bucket or scoop mixing with another chemical can react. Dirt, dust, leaves and any liquid can cause a volatile reaction when mixed with pool chlorine.

chemical storage area sign for poolsTrust me when I say that chemical fires are extremely hazardous, as I have conducted many flammability experiments on our pool chemicals. Chlorine mixed with any other chemical or foreign substance can emit toxic gases, erupt in flames, explode, or all of the above.

Keep Pool Chemicals Clean, Closed, Dry and Separated. 

Be Careful America, because ‘Oxidants Happen!’.  😉


Dr. Pool



Bad Pool Chemical Combinations — 12 Comments

  1. Hi.
    I need help figuring out what pump to buy.

    My pool dimensions are 25 long by 10 wide (kidney shaped) & it is 3′ deep in the shallow & almost 5′ in the deep end.

    I also have a million trees that drop leaves & flowers & even berries into our pool.

    I was told at a store that getting too much of a motor or too heavy duty a pump I will have just as bad effect. We have found great success w/ a pentair sand shark auto cleaner but after a recent hail storm our motor just isn’t working how it used to.
    Tina from Texas

    • Hi Tina, the way to select a pump is to match the pump flow rates (in gallons per minute GPM), to the filter design flow rate. Look on your filter label for this information, or find it on a product page (where we sell the filter that you have). Then, look for a pump that will produce that level of flow rate that works best with your filter. Too much flow is much worse than too little flow, in terms of filtration – but you need enough flow to ideally, filter all of the water in the pool, in an 8 hour period. For example, a 50 gpm pump can pump 50 gallons per min. or 3000 gallons per hour. In 8 hours, it will pump 24000 gallons. Your pool is much smaller, if your dimensions are correct. If your previous pump make/model/size worked well, it is easiest to replace with the same. If you want more flow or need more flow, proceed cautiously, to not go too big. Your pump, which stopped working “how it used to”, after a hail storm… could have a clogged impeller, or an air leak in front of the pump, and could possibly be repaired instead of replaced.

  2. Hi, I have had issues with my (pebbletec) pool turning blue along the tiled water line as well as the creepy. I’ve concluded it’s too much copper (from algaecide and copper trichlor additive) and which is leaching out somehow? Or maybe you have a better notion? Thanks!

    • Hi Phil, copper would be a good guess, especially if it is a stain, and not a gooey, oily deposit. The only other guess would be some blue substance (paint?) that was thrown in the pool by a prankster. Not much else makes a blue stain. You can test the water with a copper test kit to confirm. Pouring an acid mixture from a flower watering can, or spraying from a spray bottle would be the trick to try and remove the stain – lower the water first, then readjust pH afterwards.

  3. Hi Dave,

    I have an interesting senario for you!!! We went away on holiday last week. We left out 18′ round above ground pool on a timer for the sand filter for 6 hours a day from 10-4. It had its solar cover on the entire time. Our neighbours said it went green about 5 days after we left. After checking levels, free chlorine is high, stabilizer low, and pH low to normal, alkalinity normal and hardness normal. Pool has a huge algae bloom. What do I do??? From what I read, it seems impossible to have low stabilizer and high chlorine! What is going on and how do I fix it!!!

    • Maybe a power outage, from storms, could’ve shut off the pump for a few days? The solar cover on top, maybe not the cause, but could aid in an algae bloom. Algae normally can’t grow with VERY high chlorine levels, unless phosphates/nitrates are very high, but a pool can still be green with 5+ ppm of chlorine testing… The filter could’ve become dirty and clogged, or if the pool was being maintained (by the neighbor?), they may have reinstalled the filter incorrectly, or did something incorrectly, to reduce filtration, or sanitation, or both. If the pool is still green, add more chlorine, until it turns a blue/gray color, and filter 24/7 until clear.

  4. I have a 650 gallon pool. How much shock/etc, and how often, should I be treating it? The kit I bought only explains amounts for larger pools. Also, should we keep the pump running constantly? We’ve been just running it for a few hours here and there or while we’re in it. Thanks!

    • Hi, most chemicals give dosage amounts per 10,000 gallons. You can multiply treatment dosages by 0.065 to obtain your dosage amounts (for a 650 gallon pool). You can also use, which I find useful. Your filter is very small, and I would run the filter much longer personally, like 12 hours per day, on a small plug-in timeclock, or at least 8 hours per day. I like to turnover the water twice, (a turnover is when all 650 gallons have been filtered). Depending on the pump flowrate, that could take some time. It is a balancing act of filtration, sanitation and circulation, that will keep your water clear and healthy. If you don’t run the filter enough, you will need more chlorine, or vice-versa.

  5. I need help with my chemicals? My pool water is cloudy, it’s a 5000 gal above ground steel
    Frame pool. I am emptying about half of the water and refilling it with new water, how do I keep it from happening again? Need help?? Thank you

    • Hi Ed, it could be your filtration, and not your chemicals, or a bit of both. Your pool may have a very small filter, and when it gets really hot outside, you may need to run it 24/7. You may also need a new cartridge, they only last a few months – using a clarifier could help your filter out. Second tip, keep the pH on the low end, around 7.2-7.4, and keep the chlorine at 1.5-3.0 ppm. If the sun burns it off too fast, add 1-2 lbs of stabilizer (cyanuric acid) – as a sunscreen (but check level first, needs to be 20-50 ppm).

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