It’s not too far a leap to say that cyanuric acid, otherwise known as pool stabilizer, is just as critical for pool water chemistry and safety as chlorine. After all, without it, chlorine would rapidly degrade under the sun’s UV rays, causing the need to replace it nearly constantly, driving up your chemical costs, and weakening its ability to disinfect. Thankfully, cyanuric acid can bind to chlorine molecules and form a protective layer around them so that doesn’t happen, while still allowing them to do their job of sanitizing pool water.
However, like all pool chemicals, there’s an ideal range for cyanuric acid and letting it get too high is also a recipe for unsafe water. If you find your pool in this situation, you’ll need to take steps to reduce cyanuric acid. Unfortunately, in our decades of experience, “cyanuric acid reducer” products haven’t proven to be effective. Ahead, learn what we recommend doing instead.
As we mentioned, cyanuric acid protects chlorine from being rapidly degraded by the sun’s UV rays. In the right range—typically 30 to 40 ppm (parts per million) for most commercial and public pools—it ensures chlorine remains active long enough to sanitize the water. But cyanuric acid itself doesn’t degrade at the same rate as chlorine does. Which means you have to be careful about monitoring and maintaining its levels too. Especially because when CYA levels climb too high, the consequences can quickly affect water quality, safety, and compliance with health regulations.
Too much cyanuric acid leads to a phenomenon often called “chlorine lock,” where chlorine becomes less effective even if test kits show adequate free chlorine levels. This means algae, bacteria, and other contaminants can survive longer in the water, even in pools that seem well-maintained.
Public pools are especially susceptible to the spread of waterborne illnesses. When chlorine is hindered by high CYA levels, the kill time for pathogens increases significantly. This reduces your pool’s ability to protect swimmers from harmful organisms like Cryptosporidium or E. coli.
Many health departments regulate maximum allowable CYA levels in commercial pools. Exceeding those limits can lead to fines, mandated closures, or even long-term shutdowns.
High cyanuric acid can lead to murky or cloudy water and even cause scaling or staining on pool surfaces, particularly when combined with other chemical imbalances. This not only creates a poor aesthetic but may also lead to costly surface damage over time.
When CYA levels creep above 50 ppm—or worse, over 100 ppm—it’s time to act. Unfortunately, unlike other pool chemicals, cyanuric acid doesn’t break down easily. It’s persistent in water, and reducing it requires proactive steps.
Aluminum sulfate is the active ingredient in products labeled as “FLOC” and is sometimes marketed as a “cyanuric acid reducer.” While we’ve written about this method before and there have been some early successes from pool service teams, this method is also complex, and really only an option if you are employing or contracting a professional pool service team to use it. Aluminum sulfate is temperamental with water temperature and pH. If your team is going to use this method, these are the steps:
As noted, this treatment should only be done by pool professionals. It may also take several days of circulation to get the cyanuric acid reduction results you’re after.
The most common and reliable method is to drain a portion of the pool water and replace it with fresh water. Because cyanuric acid is dissolved in water, the only guaranteed way to remove it is to remove the water containing it.
How it works:
This method is a good one because it’s effective and predictable and has no chemical side effects. However, anytime you have to drain a pool, even partially, it’s time-consuming, disrupts pool operations, and can lead to the loss of business for those days the pool needs to be closed. A pool drain can also be impractical for large pools, and for pools in dry climates, such as Arizona, you may face drought restrictions that limit how often you can drain a pool, even partially.
There are essentially two ways you can add cyanuric acid to pools. You can either add it separately, on its own, and add what’s called “unstabilized chlorine” or liquid chlorine separately. You can also buy a combination product called “stabilized chlorine,” which contains both the cyanuric acid and the chlorine together. These are often sold in convenient tablets or ‘pucks’, so because of that ease of use, they’re a popular choice for many pools.
However, this creates a foundational issue: because cyanuric acid doesn’t degrade like the chlorine, what many pools end up doing is add far too much too often, simply by using a combined product. In other words, the chlorine will still degrade and you will need to add more throughout the pool season. If you are continuously adding cyanuric acid with that chlorine through a “stabilized chlorine” product, you’ll be building up your cyanuric acid levels unnecessarily high.
The best method to keep cyanuric acid levels in the ideal range is prevention, and the best way to prevent too high levels is to regularly test cyanuric acid levels in addition to chlorine and add cyanuric acid separately from unstabilized chlorine. This will give you far more control over how much you’re adding, and with it, their overall levels.
Done this way, most pools will only need to add cyanuric acid once at the beginning of the outdoor pool season.
Then, you can follow a few key steps to keep levels in range throughout the season and prevent the need to dilute or drain pool water:
Whether you're managing pools at hotels, apartment complexes, HOA communities, or typical commercial or public facilities, having a Certified Pool Operator (CPO) on staff is always a smart move. Not only are they trained in pool chemical safety and calculations, but in many areas, a CPO is required by the local health department for pool operation.
That said, managing the right balance of cyanuric acid and free chlorine levels can still be complex and time-consuming. That’s exactly why we created the Pool Shark H2O app. It handles all the chemical calculations instantly, showing you the precise amounts of cyanuric acid and other chemicals to add—helping ensure water safety, chemical balance, and lower costs.
When used with the LaMotte Water Link Spin Touch, testing takes just 60 seconds and delivers highly accurate results.
Plus, all tests and chemical logs are automatically recorded and locked digitally, making Health Department compliance easier than ever. Managers can also view test results, logs, and alerts remotely—across multiple properties—from one centralized platform.