Help! Rain + pool = green

[texsn95]

Get it tested at a store and post up the test results. Ask them to test for phosphates too. But yes you were probably already on the verge of an algae bloom, and the rain diluted the free chlorine enough to let it blow up. Let me guess..you use the 3" trichlor pucks in a chlorinator?

[texsn95]

A snippit of helpful info. I add ~20oz of 10% liquid shock (bleach) daily for my chlorination, and have my chlorinator set at the very minimum to replinish the tiny amount of CYA I lose by splashout or backwashing (keep it around 50). I got tired of fighting the high CYA issue by using the 3" pucks, and now my water has never been so clear with 0 algae.

High Cyanuric Acid & High Free Chlorine

As you already know, CYA is the stabilizer for the chlorine. Call it cyanuric acid, stabilizer, conditioner... it's all the same thing.

There needs to be a balance between the chlorine and CYA. The CYA needs to be 7.5% of your chlorine level. This means if you run the chlorine at 2.5ppm (1.5 - 3.5ppm is optimal), your CYA is 7.5% of 2.5ppm. 2.5 divided by 7.5% = 33.

As the CYA rises through Trichlor puck and Dichlor chlorine use, the chlorine must rise as well to meet the CYA demand. Too high or low CYA and the chlorine is rendered pretty much useless. You have a 150ppm CYA. This means to have the chlorine be effective, you'll need to run the chlorine at 11ppm. 11 divided by 7.5% = 146.

This is a huge problem that many pool owners face. They simply want to shock the pool and may not understand the relationship between CYA and chlorine. They also get their information from pool store employees who think they know, but many times don't.

Now, the only way to reduce the CYA is to do a partial drain and refill. Your CYA is up so high that even if you drain 2/3 of the water and refill, the CYA will still be at the highest acceptable level, 50ppm. If you use Trichlor pucks to dose the pool through the week, the CYA will slowly rise again and you'll be in the same situation.

If you simply shock the pool and possibly clear it up, you're going to be in the same situation you're in right now. The CYA is still too high and eventually the chlorine will be ineffective. You just wasted all that time, money, and chemicals because you're eventually are going to need to do a drain and refill.

Your best bet is to do a full drain and refill, then balance the chemicals out. Test the fill water so you know what the starting point is. You won't get a CYA reading on a newly filled pool so you need to shock the pool with Dichlor. This is a stabilized form of chlorine and will get the CYA in the pool. When you reach the 30 - 50ppm mark, stop and use regular liquid chlorine. You can either use liquid chlorine.

Be careful when using Dichlor as it can get out of hand quickly.

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.

Relationship between CYA and FC

Chlorine / CYA Chart • Pool School • Trouble Free Pool

Pool calculator

The Pool Calculator

[Reefmonkey]

The rain is lowering the pH in your pool as well as diluting the chlorine. Algae love lower pH. Don't just shock the pool, also add sodium carbonate.

[fordlover]

I'd venture to guess that your filter may not be working effectively. My parent's were strugling to get their pool to clean up, turned out that a manifold in the filter was cracked allowing probably 90% of the water to bypass the filters. Once they got it replaced the pool cleared up about 10 hours later.