Cyanuric acid (CYA), also called stabilizer or conditioner, is one of those pool chemicals that a lot of people don't think about until something goes wrong. When it gets too high, your chlorine essentially stops working — and no amount of shocking will fix it until you address the CYA first.
CYA protects chlorine from being destroyed by UV rays. Without it, sunlight can burn off your free chlorine in a matter of hours. That's why stabilized chlorine tablets (trichlor) contain CYA built in — every tablet you add is also adding a small amount of stabilizer.
The problem is that CYA doesn't evaporate or break down. It only leaves the pool when water is drained. So over time, especially if you use trichlor tablets regularly, CYA builds up.
⚠️ Above 100 ppm, CYA starts significantly reducing chlorine effectiveness. Above 150 ppm, your chlorine is nearly useless regardless of how much you add. This is called "chlorine lock."
Here's the honest answer: there's no chemical that removes CYA. The only reliable way to lower it is to drain some of your pool water and refill with fresh water. The amount you need to drain depends on how high your CYA is.
Use this as a rough guide:
After refilling, test and rebalance all your chemistry before swimming.
💡 Switch to unstabilized chlorine like liquid chlorine or cal-hypo shock instead of trichlor tablets. Trichlor adds CYA every time you use it. Liquid chlorine adds none.
PoolBoy logs your CYA readings over time and alerts you before it gets out of range — and tells you exactly how much water to drain based on your pool size.
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