Why Do I Have Cloudy Pool

by Jeff
(CA)

I have a small pool, probably 10-12000 gallons with some kind of coating on it. I think its fiberglass. It was completely full of algae and the bottom was not visible. It had no chlorine, the pH was a little high, and the CYA was over 100.

I put in a case of chlorine, a little less than a quart of acid. I netted it out and brushed it down. I cleaned out the filter (cartridge) and then let it run for 8 hours. The water went from cloudy green to cloudy white and now more of a cloudy bluish white.

I still cant see the bottom. Cleaned out the filter again a few days later and its still cloudy. It's going through chlorine fast. The pH is 7.1 now. Why is it still cloudy?

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Thanks for the question Jeff

The reason the pool is cloudy is because the chlorine is killing the algae. The water will always go from green to a white/grey cloudy as the chlorine will begin to hold better. However, you have another issue, and that's the high CYA. There's a relationship of CYA/chlorine that needs to be met. The chlorine is 7.5% of the CYA. The range for CYA is 30 - 50ppm. If your CYA is at 100ppm, you need to run the chlorine at 7 - 8ppm to have it effective.

You have 2 choices. You can either keep shocking the pool until the chlorine only loses

1 - 2ppm between applications then keep the level at 7ppm, or you need to drain 2/3 of the water, refill, and balance everything out again.

Once the pool goes cloudy and you lose only 1-2ppm between shocks (you need to test between shocks, 8 - 10 hours of filtering) you know the algae is dead. Now it a matter of filtering and changing out the cartridge. Shocking is a process, not an event. The trick is to get AND keep the chlorine above 10 - 12ppm for a period of time. You'll need to manually dose the pool with chlorine to keep it at 10 - 12ppm.

Do not use Dichlor chlorine to shock the pool when you already have CYA in it. This is a stabilized form of chlorine and should only be used for new fills. For every 10ppm of chlorine added with Dichlor, you'll raise the CYA by 9ppm. For every 10ppm of chlorine added with Trichlor tabs you'll raise the CYA by 6ppm.

It can take up to a week or longer of constant filtering and changing the cartridges before the water is clear. With a CYA of 100ppm or greater I'd encourage you to do a 2/3 drain and refill. This is the best long-term solution. If you choose not to do this, just remember that once the pool is clear you're going to need to keep the chlorine between 7 - 8ppm with a CYA of 100ppm.

Robert