Drain and refill is the reliable way
Cyanuric acid does not break down or get consumed, so it builds up and stays. The only dependable way to lower it is to drain part of the pool and refill with fresh water, which dilutes it. To halve your CYA, you replace roughly half the water; to drop it by a third, replace about a third.
There are products that claim to reduce CYA, but results are inconsistent and they are not a trustworthy substitute for a partial drain. When CYA is genuinely too high, replacing water is the fix that works.
Why high CYA is a problem
Cyanuric acid protects chlorine from sunlight, which is good in small amounts, but it also weakens chlorine. The more CYA you have, the more free chlorine you need to keep the same sanitizing power. Let CYA climb high enough and the chlorine level required to stay safe becomes impractical to hold.
This is why a pool with high CYA keeps going cloudy or green even though there is chlorine in it: the chlorine is there but too weak for the stabilizer. See the ideal levels for the free chlorine to CYA relationship.
Stop it from climbing again
CYA usually creeps up because of the chlorine you use. Dichlor granular shock and trichlor tablets both contain cyanuric acid and add it every single time. If you chlorinate with those, your CYA rises all season until you have to drain.
The fix is to switch routine chlorination to liquid chlorine or plain bleach, which add no CYA. Use the chlorine calculator for liquid dosing, and check your CYA with the cyanuric acid calculator when you do add stabilizer on purpose.
Know your target
Most chlorine pools want CYA in the 30 to 50 ppm range; saltwater pools usually run higher, around 60 to 80, because the generator makes chlorine slowly and needs the extra sun protection. If you are well above your target, plan a partial drain, and going forward, only add CYA deliberately to hit the range rather than letting tablets pile it on.
Frequently asked questions
How do I lower cyanuric acid in a pool?
By replacing water. CYA cannot be removed with chemicals reliably, so you drain part of the pool and refill with fresh water to dilute it. To roughly halve your CYA, replace about half the water. Products that claim to reduce CYA give inconsistent results and are not a dependable substitute.
Will any chemical lower cyanuric acid?
Not reliably. There are CYA-reducing products on the market, but their results are inconsistent, so they are not a trustworthy fix. The dependable way to lower cyanuric acid is a partial drain and refill with fresh water.
Why does my cyanuric acid keep rising?
Because of the chlorine you use. Dichlor shock and trichlor tablets both contain cyanuric acid and add it every time you use them, so CYA climbs over the season. Switching routine chlorination to liquid chlorine or plain bleach, which add no CYA, stops the climb.
What is a high cyanuric acid level?
Above your target range, which is 30 to 50 ppm for most chlorine pools and 60 to 80 for saltwater pools. The higher CYA goes, the more free chlorine you need to stay sanitary, until it becomes impractical to hold. Very high CYA is a common cause of a pool that will not stay clear.
Does cyanuric acid go away on its own?
Barely. CYA is very stable and is not consumed by sanitizing, so it does not break down meaningfully over a season. It only drops when you dilute it by replacing water, or slowly through splash-out and rain refilling with unstabilized water.