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3 Ways To Lower Cyanuric Acid In A Pool (Reduce High CYA)

Cyanuric acid is a weak acid that reduces chlorine loss in your pool water by shielding it from the sun’s UV rays, effectively “stabilizing” your chlorine. It also goes by the name CYA, pool stabilizer, or pool conditioner.

The ideal range for cyanuric acid in your pool is between 30 and 50 ppm (parts per million). Anything significantly higher and you should be keeping a close eye on your water chemistry, as it may be compromised.

Let’s talk about why this happens, why it matters, and how to lower cyanuric acid (CYA) in your swimming pool.

Why You Have High Cyanuric Acid

It’s chlorine’s job to keep your pool water clean, but depending on which type of chlorine you use, it may or may not contain cyanuric acid. Stabilized chlorine has CYA built-in, whereas unstabilized chlorine doesn’t.

Heads up: Dichlor and trichlor are stabilized types of chlorine, and sodium hypochlorite (liquid chlorine), lithium hypochlorite and calcium hypochlorite are unstabilized.

The main reason for high CYA levels in your pool is from using too much stabilized chlorine. When the pool water evaporates, CYA remains in the water, much like other chemicals such as salt and calcium.

As an example, 1 lb. of trichlor in a 10,000 gallon pool will raise the CYA level by 6 ppm. With the ideal range for pool CYA being 30 ppm to 50 ppm, it’s easy to see how this level can quickly spike.

Why High Cyanuric Acid Is Bad News

Having high CYA in your pool can lead to a few problems with the pool water:

  • Inaccurate total alkalinity readings. High CYA can return false total alkalinity readings, because it can falsely contribute to your carbonate alkalinity (which makes up your total alkalinity). Balancing your water according to the Langelier Saturation Index will let you know precisely where your chemical levels are.
  • Stalls chlorine effectiveness. High CYA will weaken your pool’s chlorine and keep it from doing its job. Referred to as chlorine lock, this happens because high CYA overpowers the free chlorine level in the pool. With compromised chlorine you’ll soon start seeing issues like algae and cloudy water.
  • Plaster problems. High CYA usually correlates with low pH because the ineffective chlorine can throw off the pH level. So, if you have a plaster finish on your pool, the water will gradually eat away at it. Damaged plaster can be repaired but it’s a process that requires your entire pool be drained.
  • Decreased ORP readings. ORP (oxidation reduction potential) measures the water’s oxidizing capacity. When too much CYA is present, you’ll see a decrease in the ORP of the water as it becomes less effective.

How To Lower Cyanuric Acid In A Pool

There aren’t any easy fixes available for a high CYA level in your swimming pool, but there are still a few things you can do.

Method #1: Drain Or Dilute Your Water

In most cases, diluting or draining the pool is your best course of action.

While the general consensus is to keep your pool full in order to avoid it popping out of the ground, swapping out water can be done incrementally in the form of partial drains.

Some people wait until it rains to take advantage of Mother Nature, but we don’t recommend doing this. The acidic nature of rain water can upset the balance of the pool, diluting the chemicals and using up its chlorine.

Here’s how to do it:

  1. Start by testing the water so you know where your CYA levels stand. You can do this using test strips, a liquid test kit, or a digital test kit. This will give you a starting point so you’ll know how much water needs to be diluted.
  2. You can drain the pool using either a submersible pump, or by using your pool’s filtration system. We recommend using a submersible pump to avoid damaging your system.
  3. If using a submersible pump, place it in the pool and attach a hose to it that is long enough to reach the drainage point/sewer you are emptying the water to. Make sure the electrical cord is long enough to reach the power outlet as well.
  4. If using your pool’s filtration system, set the valve to drain/waste/backwash. The risk here is that if you drain too much, the water level will fall below the skimmer. The skimmer will then only take in air which can damage your system.
  5. Slowly drain the pool a few inches. Don’t drain too much! Using a garden hose attached to your outdoor spigot, refill the pool to the halfway point of the skimmer.
  6. Retest your water. Repeat the process until the CYA levels have dropped to between 30 and 50 ppm.

Method #2: Use A Cyanuric Acid Reducer

A product such as Bio-Active or Natural Chemistry is a CYA reducer that will help lower cyanuric acid in your pool.

In cases where the CYA level is extremely high, you can use CYA reducer to bring it down, and then use the dilution method to top it off. These products are also pretty simple when it comes adding to your pool water.

Important: you should never add algaecides, phosphate treatments, or clarifiers to the pool for 7 days prior to using a CYA reducer.

Here’s how to do it:

  1. The day before (and day of) using a CYA reducer, the pool has to be at least 65°F. Also, you’ll need to test the water to ensure the chlorine is between 1 and 5 ppm, the pH between 7.2 and 7.6, and total alkalinity between 80 and 120 ppm.
  2. There are two sizes you can purchase: an 8 ounce pouch for up to 25,000 gallons, and a 16 ounce pouch for up to 50,000 gallons. Choose your pouch.
  3. Using a 5 gallon bucket, fill it up halfway with water and dump the CYA reducer powder into it. Mix it up using a wooden stir stick.
  4. Walking around your pool, slowly pour the solution into the water. Close to the returns jets is ideal so it gets dispersed faster.
  5. CYA reducer is very safe, so you can use the pool immediately after adding it. 
  6. Wait between 7 and 10 days to retest the pool for CYA levels. If they’re still high, repeat the process.

Method #3: Use Specialized Filters

Another option, even if a bit on the expensive side, is to use a specialized cleaning filter like reverse osmosis.

Reverse osmosis works by sending the pool water through an ultra-fine, semi-permeable membrane, then into a large pressure tank where it’s filtered with activated charcoal, before the water is sent back to the pool.

A drawback of RO is the amount of water that gets wasted, with 2 gallons wasted for every 1 gallon that’s filtered. But RO has added benefits of lowering calcium hardness as well as total dissolved solids – both of which stay present in the water until it’s swapped out.

Using a RO system is ideal for those in regions where water restrictions/shortages are in place, and a single treatment can last for years. Hiring a professional for the service costs around $500, and installing an RO system will run you close to $2,000.

How To Bring Cyanuric Acid Back Up

After using any of the above methods and retesting the pool, you may realize you’ve taken out too much cyanuric acid.

If your CYA level is below 30 ppm, you can raise the amount of cyanuric acid by using stabilized chlorine, or by simply adding cyanuric acid (usually found as pool stabilizer or pool conditioner). 

The latter is usually preferred, as using CYA in addition to unstabilized chlorine allows you more control over the individual aspects of your pool chemistry.

As a general rule, 13 ounces of CYA should be added to a 10,000 gallon pool to raise its level by 10 ppm.

Reducing CYA: Simplified!

Learning how to lower cyanuric acid in the pool is a bit of a learning curve, but once you wrap your head around it, it’s not too hard to do.

With 3 options to choose from, you can quickly rid the pool water of that excess acid, restoring it to its former glory.

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