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What Is Pool Stabilizer?

By Matt Giovanisci | Updated: July 3, 2019

You spend a lot of time and money buying and adding chlorine to your pool, and then testing to make sure the levels are just right for keeping your water clean, and your pool safe for family and friends. So the last thing you want to do is leave it vulnerable to the elements.

The sun can destroy your sanitizer by causing it to evaporate before it can clean your water. You can’t exactly move your pool inside, but you can add a pool stabilizer to counter the sun’s effects, and keep your chlorine levels, well, stable.

What Is Pool Stabilizer?

Also known as pool conditioner, chlorine pool stabilizer, or chlorine stabilizer you can buy this chemical additive as either liquid or granules.

It’s also often called cyanuric acid, a chemical that may be included in chlorine tablets or sticks (called trichlor) or shock (called dichlor). When they’re mixed together in shock or tablets, the resulting product is called stabilized chlorine.

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Typically, you won’t need to add any extra stabilizer separately if you’re using one of the combination products. In fact, if you add too much, you might develop a problem called “creep,” which describes the stabilizer chemical’s tendency to build up to problematic levels over time. Too much of any chemical in your pool is never a good thing.

If your pool stabilizer levels creep too high, it can reduce the effectiveness of your sanitizer, or in other words, do the exact opposite of what it’s meant to do.

The only way to lower stabilizer levels in your pool is to remove some of the water, and add clean water. Once you do that, you’ll have to balance all your chemicals again.

What Chlorine Stabilizer Does

In the simplest of terms, pool conditioner helps your chlorine stay in the water longer. More specifically, it binds to chlorite ions (your free chlorine), making them impervious to the sun’s rays. Without it, ultraviolet rays would break apart the chlorite ions, allowing the chlorine to evaporate into the air. It literally stabilizes the ion.

Your free chlorine will then be available for sanitizing three to five times longer than it would be without using stabilizer.

But that longer lifespan comes with a bit of a catch. When stabilizer forms a bond with chlorine, its sanitizing ability, which goes by the fancy name Oxidation Reduction Potenial (ORP), is somewhat hindered. In other words, it takes stabilized chlorine longer to kill bacteria than it takes chlorine without stabilizer.

In fact, if you also have a hot tub, this is the reason you absolutely should not add stabilizer to your spa. The bacteria that causes folliculitis, Pseudomonas aeruginosa, takes 100 times longer to be eliminated from a spa with stabilized chlorine, leaving you and your hot tub guests vulnerable to infection.

The good news is as long as you maintain proper free chlorine levels, stabilizer is incredibly helpful in extending the life of your chlorine, helping maintain proper pool chemistry, and saving you money.

How Much Pool Stabilizer Should You Use?

You’ll find wide variations among recommendations for the optimal levels of stabilizer in your pool, from a few parts per million (ppm) to 100 ppm, and everything in between.

We recommend nothing higher than 50 ppm. At that concentration, the difference in chlorine effectiveness between pools with stabilizer and without becomes noticeable. You may also see more algae growth at levels above 50 ppm due to the negative effect on your free chlorine.

Just to reassure you even further, stabilizer levels above 50 ppm do not provide any significant increase in UV protection for chlorine, but they do increase the risk of bacteria and algae growth.

With your pool stabilizer at 50 ppm or lower, you’ll still want to monitor your available chlorine through regular, frequent water testing to ensure your pool is properly sanitized.

To maintain a healthy balance of free chlorine and stabilizer, aim to keep your sanitizer levels at 7.5 percent of your stabilizer level. This means if your pool conditioner is 50 ppm, you’ll want the free chlorine level to be around 3 ppm, the ideal level in any case.

Warning: One exception to the recommended levels of chlorine stabilizer must be made in the event of cryptosporidium contamination. Cryptosporidium, also called crypto, is a parasite sometimes introduced to pools through fecal contamination, and it’s highly resistant to chlorine. You may sometimes hear about municipal pools or splash pads being closed “due to crypto contamination,” which requires serious intervention to eliminate.

Due to the parasite’s ability to survive under normal chlorine levels, if you encounter this type of contamination in your pool, you must lower your pool stabilizer levels to a maximum of 15 ppm before hyperchlorinating. You’ll also need to backwash or replace your filter and balance the water before letting anyone back into your pool.

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When to Use Chlorine Stabilizer

Does adding chemicals to your pool once a year sound too good to be true? Well, it is—except in the case of pool stabilizer. Because the chemical doesn’t get used up while working, nor does it gas off like other pool additives, it simply remains in your water.

The levels typically won’t ever decrease unless you have significant splashout or evaporation, requiring you to add water. Dilution (whether from rain or top-off) will also lower stabilizer concentration in your pool.

When you use stabilized chlorine in your pool every week, you’re adding a touch of stabilizer every time you add chlorine. You really won’t need more than that throughout the year to keep pool stabilizer at the appropriate concentration.

However, it’s because of this that pool stabilizer levels can creep up over time, particularly if you don’t need to top off your pool very often. Buy quality pool chemistry test strips, and you’ll be able to keep an eye on your stabilizer level when you test your water each week.

If you notice your stabilizer level creeping up, check your water level. Topping off your pool may be enough to knock it back down a bit.

You may also switch to non-stabilized chlorine, which comes in liquid and granules. Just be sure to monitor your water chemistry, so you can switch back or add stabilizer as needed.

How to Add Pool Stabilizer

Some pool chemical instructions tell you to add them at the filter, while others may be poured straight into the pool water. When it comes to pool stabilizer, you don’t want to do either of those, even if the instructions say it’s okay.

Remember that pool stabilizer is an acid. The chemical dissolves very slowly, so slowly, in fact, that the acidity can damage your pool surfaces or skimmer if left to sit there and dissolve in its own time.

We recommend buying a five-gallon bucket, filling it with water, then dissolving the stabilizer in that water. This way, whether it takes ten minutes or an hour to dissolve, you won’t be damaging expensive pool surfaces or delicate circulation parts by leaving an undiluted acid lying around on them.

When and Why to Avoid Chlorine Stabilizer

You already know you should definitely never add conditioner to a hot tub, and you could probably guess that indoor swimming pools won’t benefit from pool stabilizer because they aren’t typically directly exposed to UV rays.

But is there any compelling reason against using a pool stabilizer in outdoor pools?

Nope. Not a one. If you own an outdoor chlorine or saltwater-chlorinated swimming pool, proper stabilizer use will save you time and money on sanitizing agents.

Sure, too much stabilizer can cause problems. Just be sure to keep an eye on it every week along with chlorine concentrations to ensure proper pool chemistry.

You’ll rest easy knowing your pool is safely swimmable for your whole family—without having to add extra chlorine for every hour of sunshine.

Happy Swimming!

Matt Giovanisci is the founder of Swim University® and has been in the pool and spa industry since 1995. Since then, his mission is to make pool and hot tub care easy for everyone. And each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.
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