How much pool water can I safely drain at once?

It is generally safe to drain up to 1/3 of your pool's water. Draining more can risk structural damage or 'floating' in high-water-table areas.

CYA Drain & Refill Calculator

Lower your Stabilizer (Cyanuric Acid) levels safely. High CYA makes chlorine ineffective; find out exactly how much water to swap.

Why is High CYA a Problem?

Cyanuric Acid (CYA) is "sunscreen" for chlorine. However, if levels exceed **100 ppm**, it causes "Chlorine Lock." This means your chlorine is present but cannot kill bacteria or algae, leading to a green pool despite high chlorine readings.

Warning: CYA does not evaporate. It only goes up when using "stabilized" chlorine like 3" tablets (Trichlor) or Shock (Dichlor). The only way to lower it is to drain and refill.

How to Use This Calculator

Enter your current test result and your desired goal (usually **30-50 ppm** for non-salt pools). The tool will show you what percentage of your pool water must be replaced with fresh water.

Pro Tip: Saltwater pools can tolerate higher CYA levels (up to 70-80 ppm) than traditional chlorine pools. If you have a salt system, use our Pool Salt Calculator to balance your salinity after refilling.

Frequently Asked Questions

Does Cyanuric Acid evaporate?

No. Unlike water, CYA stays in your pool. The only way it leaves is through splash-out, backwashing, or physically draining and replacing the water.

Can high CYA damage my pool?

High CYA doesn't directly damage the pool structure, but it makes your chlorine ineffective. This leads to algae growth (Green Pool), which can stain plaster or clog filters.