Bad Pool Chemical Combinations

Written By Timothy Te

22nd December 2020

Contrary to what many people say, our pools are not chemical soups that need as much chemicals as possible to be clean and clear. Believe it or not, there are actually combinations of pool chemicals themselves and pool chemical levels that can not only damage our pool, but are downright dangerous.

Bad Pool Chemistry Combinations

While we always advocate having the perfect water balance at all times to keep your pool as clean and clear as possible. If this is followed, then this post wouldn’t be needed, but there will always be times that we forget to dose our pools or there will be weather issues that will swing our water chemistry in unexpected directions. So here are some bad pool chemistry combos that will give you

Low Chlorine + Low Stabiliser

Well, if we’ve learned anything over the years, it’s that low chlorine levels and low stabiliser levels are a recipe for disaster when it comes to your pool. With low stabiliser levels, your pool chlorine won’t have any protection from the UV rays, and couple that with low chlorine levels, will equal to zero chlorine levels before long. And if there’s no pool chlorine, you’re looking at algae blooms at the very least and contamination by bacteria at the worst.

High Stabiliser + Low Chlorine

While sabiliser protects your chlorine from the sun’s UV rays, a too high stabiliser level coupled with a low chlorine level is pretty much equal to having no chlorine in your pool as stabilisers also reduce the efficiency of your pool chlorine. This can also lead to a condition called a chlorine lock.

High pH + Low Chlorine

As we’ve explained in our Pool Chlorine and pH Relationship post the higher the pH levels of your water, the less effective your pool chlorine is. This is the perfect pool chemistry combination for algae blooms because algae loves high pH levels and it’s constantly looking for an opening in your chlorine levels to start breaking out!

High pH + High Calcium

High Calcium levels and high pH levels will lead to cloudy water and scale formation on your water lines and on the insides of your pipes. Not only are scales unsightly, but they can also cause clogs and blocks on your pool equipment as well. A very visible symptom of this bad pool chemistry combination is finding white chalky residue wherever pool water splashes have dried out.

Low Alkalinity + Low pH

If you have this pool chemistry combination then you wouldn’t have to worry about algae blooms, as low pH is very bad for algae and makes your chlorine much more effective. But that’s not saying that this is good though, you’re just trading one problem for another. A combination of low pH levels and low Alkalinity is very acidic which is corrosive and may damage your pool surfaces and equipment, not to mention very irritating on the skin as well.

High Stabiliser + High Chlorine Levels

Now this is usually caused by the constant use of stabilised chlorine to top up pool chlorine levels. Once stabiliser has reached the high levels (over the recommended levels of 50ppm) your pool chlorine starts to lose its potency, requiring higher and higher chlorine concentrations to properly sanitise the pool. This combination makes chlorine testing very unreliable and what may seem like fine chlorine levels can actually be ineffective.

These pool chemistry combinations are some of the worst that can happen to your pool, so don’t forget our mantra here at Mr Pool Man, test, test, and test your water! The more familiar you are with your pool water, the easier you can treat these bad pool chemistry combinations. For more information on how to test your pool water, check out our ultimate guide to testing your pool water here.

Very Bad Pool Chemical Combinations

Now we’ve talked about bad pool chemistry combinations, now we’re going to talk about which pool chemicals do not play well with each other. This section is probably redundant if you follow our rule of thumb which is to add your pool chemicals one at a time and circulate in between applications, but here are what some of the very bad reactions when chemicals are added at the same time.

Chlorine Shock and Algaecide

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Chlorine shock can oxidize and destroy the chemical compounds in Algaecide when they’re added at the same time. While nothing bad will happen (no explosions or poison gas) when added together, this will be a waste of money as the shock will destroy the algaecide. When you plan to add algaecide, make sure to test your water beforehand to ensure that your chlorine levels have gone down.

Chlorine Shock and High Metal Levels

This is something that usually happens when you refill your pool with new water. The new water may have high metal levels causing your chlorine shock to react with them, magically turning your water green or at the very worse case, black streaks and stains on your pool surfaces. So a good rule of thumb is to have new water tested before adding to your pool or to use a metal sequestrant on your pool if you’re not sure about the source of your new pool water.

Sequestrants and Chlorine Shock

Yes, we did say to use sequestrants in the previous section, but as a caveat, wait a day after adding the sequestrants before adding in the chlorine shock so that it won’t affect the sequestrant before it gets a chance to circulate around the pool.

Clarifier and More Clarifier

While it doesn’t sound logical, adding more clarifiers after dosing your pool with clarifiers will actually cause the new clarifying chemicals to become something like a dispersant, causing cloudiness on your pool instead of clarifying it! So if the first treatment didn’t do its job, wait for a week before applying clarifiers again just to be absolutely safe.

Cyanuric Acid and Stabilised Chlorine

If you use stabilised chlorine then no need to add cyanuric acid to ensure that your stabiliser levels don’t go over 50ppm and vice versa. So if you use cyanuric acid, use unstabilised chlorine instead. P.S. Chlorine tablets are stabilised so make sure to monitor your cyanuric acid levels when you use chlorine tablets!

Pure Chlorine + Any other chemical

NEVER, EVER, NEVER, EVER add pure chlorine to any other chemical or as a matter of fact, never mix any pure chemical with any other pure chemical. You may get toxic gas reactions, chemical fires, explosions, or depending on the chemicals added, a combination of all three!

Pool Chemical Safety

If there’s one thing that we can’t stress enough, is always keep your pool chemicals in a cool dry place and to keep them tightly sealed to prevent spills and accidental mixing. Chemical fumes and fires are no joke. So always keep them dry and separate. Also, throw away any pool chemical that might be expired as not to clutter up your storage area. To find out more about the life expectancy of your pool chemicals, refer to our guide on pool chemical expiries to learn more.

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

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Written By

Timothy Te

Pool Guru at Mr Pool Man

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