You’ve done everything right—or so you think. You’ve shocked the pool, your chlorine levels are high, but the water is still a murky green. What’s going on?
One of the most common reasons for a green pool despite high chlorine levels is something called “chlorine lock,” often caused by high levels of Cyanuric Acid (CYA).
CYA, or Cyanuric Acid, is a stabilizer that helps protect chlorine from being destroyed by the sun’s UV rays. It acts like a time release, holding on to chlorine and releasing it slowly over time. It’s crucial for maintaining chlorine levels, especially in sunny regions like Arizona. But here’s the catch: when CYA levels get too high, it can actually prevent chlorine from doing its job—killing algae and keeping your pool clean.
Testing your pool’s CYA levels is straightforward with a liquid test kit or test strips. Ideally, your CYA should be between 30-100 ppm. When it climbs above 100 ppm, the effectiveness of your chlorine drops significantly, leading to that stubborn green water.
Cyanuric acid is an important component of pool chemistry, and it's included in any water "start-up" (i.e., the chemicals you are supposed to add when you fill your pool). Chlorine tablets also all contain CYA to help stabilize the chlorine in the tablets. But CYA does not dissipate, and it is not captured in your pool's filter. That means that CYA builds over time, and it continues to build every time you put a chlorine tablet in your pool. After 3 or 4 years, your CYA levels could have climbed by 100ppm or more, just from regular addition of chlorine tablets each week.
If your CYA levels are too high, your best bet is to partially drain your pool and refill it with fresh water. This dilutes the CYA concentration and gives your chlorine a fighting chance to clear up the algae. Remember to be careful about timing for a drain and refill - in Arizona, it's too hot in the summer, and you risk damaging plaster or PebbleTec if you drain your pool when it's hot. We recommend waiting until daily high temperatures are below 90 degrees before fully draining and refilling your pool.
Sometimes, the issue isn’t just about CYA. Here are a few other things to check:
The effectiveness of chlorine is also impacted by the pH of your pool water. If the pH is too high (above 7.8) or too low (below 7.2), chlorine won’t work as effectively, potentially leading to a green pool. Make sure to test and adjust your pH levels as part of your troubleshooting process. It's more rare that a pH imbalance will lead to stubborn algae if your chlorine is high, unless your pH levels are dramatically outside of normal range.
Even with balanced chemicals, a green pool can persist if your filtration system isn’t running properly. Ensure that your filter is clean and operating for at least 8-12 hours a day in the summer to give your pool the circulation it needs to stay clear.
Debris like leaves, dirt, and other organic material can consume chlorine and contribute to algae growth. A thorough cleaning and vacuuming can help clear out any contaminants that might be causing issues.
Phosphates are another player in this green pool mystery. They act as a food source for algae, helping it thrive even when chlorine is present. However, it’s important to note that phosphates alone rarely cause a green pool if chlorine levels are properly balanced.
You can test for phosphates with a simple kit. If your levels are high, you might consider using a phosphate remover, but this should be secondary to managing your CYA and chlorine levels.
So, what’s the game plan? Here’s a step-by-step approach to clear up your green pool:
Once your pool is clear again, regular maintenance is essential to prevent future issues. Regularly test your water, keep CYA levels in check, balance your pH, and ensure your filtration system is running efficiently. Consistent care will help you avoid the dreaded green pool and keep your water sparkling clean.
Conclusion
Dealing with a green pool despite high chlorine levels can be frustrating, but with a little knowledge and the right steps, you can get your pool back to its crystal-clear state. Remember, managing CYA and keeping your pool balanced is the key to preventing this problem in the future.
