3 Ways to Lower Cyanuric Acid in a Pool (Reduce CYA)

Is the cyanuric acid level in your pool too high?

A high CYA level (typically above 50 parts per million) can over-stabilize your chlorine and leave your pool vulnerable to things like bacteria and algae. It also inflates total alkalinity which makes balancing your pool more difficult.

This article will cover what causes a high CYA level and how to the lower cyanuric acid in your pool using various methods.

Quick answer: A partial drain and refill is the only practical method for lowering the cyanuric acid level in a pool. Products that claim to lower CYA are unreliable at best, and installing a reverse osmosis filter is simply too expensive.

What Causes High Cyanuric Acid?

It almost certainly comes from the chlorine you’re using.

Stabilized chlorine (most tablets or granular forms) contains cyanuric acid to prevent the sun from breaking it down too quickly in the water, whereas unstabilized chlorine doesn’t contain any.

Since cyanuric acid takes a long time to degrade in a pool, frequently adding stabilized chlorine to the water will slowly raise the cyanuric acid level over time, until it eventually gets too high.

Note: Liquid chlorine (sodium hypochlorite) doesn’t contain cyanuric acid or other unnecessary additives, making it a popular choice for pool owners who often struggle to keep those levels down.

How Do You Lower Cyanuric Acid In a Pool?

The bad news is, there aren’t any easy fixes for a high cyanuric acid level, but you do have multiple options to consider.

Here are 3 ways to lower CYA in your pool:

Method 1. Partially Drain Your Pool (Recommended)

In most cases, diluting the pool water is the best way to reduce your cyanuric acid or stabilizer level.

Dilution works by replacing over-stabilized water with fresh, unstabilized water. For example, if your cyanuric acid level is 30% too high, replacing 30% of your water will bring the CYA level down by exactly that amount.

This is the fastest and most reliable method, and aside from the cost of water and chemical replacement, a partial drain isn’t quite as complicated or as risky as a full drain and refill.

Before we get into the process, you’ll need to know how much water to drain from your pool. We built a simple calculator to help you figure this out:

Ready to move on? Let’s get to it.

Here’s how to do a partial drain and refill:

1. Mark your current water level by placing a strip of tape on the wall. This will come in handy later when putting water back in, and will prevent you from diluting too much.
2. If you only need to replace a small amount of water, you can set your filter valve to backwash or waste and let your pool pump do the work.
3. If you’re replacing a large volume of water or backwashing just isn’t an option, use a submersible pump instead. Place it in the pool and attach a hose long enough to reach the drainage point. Turn off your pool pump if using this method.
4. Drain the water based on the calculator result above. You may have to eyeball it as best you can if you’re backwashing, otherwise a good submersible pump will allow you to track the water in gallons.
5. Once enough water has been drained, attach a hose to your outdoor spigot and refill the water back up to the previous level.
6. Test your cyanuric acid level and run through steps 2-6 again if your CYA is still too high. The black dot test is the most accurate but test strips will also work as an alternative.

Method 2. Use A Cyanuric Acid Reducer (Mixed Reviews)

Cyanuric acid reducers like Bio-Active or Natural Chemistry are still relatively new products in the pool industry, and the reviews are still very mixed on whether or not they actually work.

They’re said to work using enzymes that break down the cyanuric acid molecules over several days — however, the effectiveness of this approach is still questionable in practice.

The selling point, of course, is that you can just dump a chemical into your pool water and it will lower your CYA. This is a very attractive proposition because it removes the need for draining and refilling your pool.

Even still, we don’t recommend using CYA reducers but we’ve outlined the steps below if you’re still set on giving it a go.

Here’s how to use it:

1. Avoid using algaecides, phosphate treatments, or clarifiers for 7 days prior to using a CYA reducer. They can interfere with this type of product.
2. Before adding any CYA reducer, make sure your water temperature is at least 65°F, and that your pool is well balanced (pH level of 7.2-7.8, total alkalinity of 80-120 ppm, and chlorine level of 1 -5 ppm).
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. While walking around the perimeter of your pool, slowly pour the solution into the water, ideally near the returns jets for better dispersion.
5. You can use the pool right away after application, but it can take 7 to 10 days to see any results. After that time, test your cyanuric acid level and repeat the steps if necessary.

Method 3. Use Reverse Osmosis (Expensive)

Another option that eliminates the need for diluting your pool is to use a specialized filter like a reverse osmosis system.

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 being sent back into the pool.

While this will absolutely lower your cyanuric acid level, it will strip out everything else that’s dissolved in the water as well. Reverse osmosis also leads to a fair amount of water wastage, which means partial refilling is still required.

The biggest drawback, though, is the cost. Hiring a specialized company to do this for you will set you back anywhere from $500 to $1,000, and installing your own reverse osmosis system will cost many multiples of that.

Overall, unless money is no object, draining and refilling your pool is still going to make a lot more sense.

The Bottom Line

A high cyanuric acid level in your pool is usually caused by simply adding too much stabilizer in the form of stabilized chlorine.

When your CYA gets too high, it will eventually weaken your chlorine and leave your pool without adequate protection against all kinds of nasty contaminants, so it’s important to deal with it quickly and efficiently.

While there are several ways to correct the stabilizer level in your pool, diluting the water through a partial drain and refill is the only reliable and cost-effective method for most pool owners.