While small levels of CYA do serve a purpose in protecting chlorine from sunlight degradation, too much can cause problems. We can help!


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The problem

Overstabilization is the buildup of cyanuric acid (CYA) in swimming pool water resulting from the use of stabilized sanitizers and stabilized shock products. It significantly decreases the effectiveness of chlorine in killing germs, bacteria and algae.

Common side effects:

- Can make your pool water unsafe

- Puts your family at risk

- Causes algae growth

- Makes chlorine less effective, decreasing its bacteria-killing power

- Will reduce the life expectancy and integrity of your pool's plaster surfaces and cause costly repairs

- Could require you to drain your pool and rebalance the water

Recommended Solutions

1. If the CYA level is >90 ppm, adjust this by partially draining some water from the pool and topping up with fresh water. Run filter for at least 24 hours until water clears.

2. Adjust the total alkalinity to 80 – 120 ppm, the pH to 7.2 – 7.8 and the chlorine to 1 – 4 ppm. Backwash or clean the filter as appropriate.

3. Continue with routine pool maintenance program. Note: Adjust dosages to suit your pool capacity. Ensure pH and chlorine levels are within the corrected ranges before swimming.

HTH® Pool Care offers granular sanitizer and shock products made with calcium hypochlorite, or Cal Hypo. Cal Hypo products do not contain stabilizer and therefore reduce the risk of overstabilizing your pool water, a condition otherwise known as chlorine lock. When your pool water is overstabilized, you will have to drain your pool water in order to remedy the situation and restabilize your pool water. As you continue with your weekly pool water care routine, use HTH® Cal Hypo products to help prevent chlorine lock as well as reduce time spent on maintenance.

As always, we’re here to help. If you have questions, contact our help line at 1-866-HTH-POOL or talk to our experts with our live chat!


Please read the following important reminders before adding pool chemicals to water:

• NEVER mix products together or dissolve before use.

• ONLY enter pool when FAC levels are below 4 ppm to prevent risk of bodily harm.