Re: So basically you add...
CYA is a bit of good news, bad news.
It will stabilize the chlorine in the pool, that is it will help reduce the effect of sunlight breaking down the chlorine. Once you have your CYA level where you want it, it is almost a set it and forget it ( for the season ) chemical. Only large scale water dumping and refilling will lower it. It does got down in the off season for in some situations for reasons the are not fully understood. Mine did not change measureabley over the winter (under ice)
The bad news on CYA is the same thing. It does not go away easily. So if you get to much you're very much stuck with it until you dilute it by doing a large scale drain and refill.
If you get your CYA level up high, (75 to 150 PPM) you will need to keep your chlorine levels high consistently and use very high levels to shock.
So, buy a box of it. Read the instructions and and enough to raise it to something like 25 PPM. It takes forever to disolve .... like a week. And this is what gets some folks in trouble. They add it in the morning and test for it in the afternoon, and add TOO MUCH because it does not show up in the test. Do not bother to test for several days. If you put it in a stocking in the skimmer you can monitor the build up and maybe pulll the stocking out when it gets up there in levels. If you broadcast it into the water and then vacuum, you will pick it up off the bottom and it will go into the filter. Then if you backwash, lots will be lost because it has not disolved yet.
The best idea, you can see then is to get some in and build it up carefully and over a couple weeks. The consenus on the forum is that the best levels are between 30 and 50 PPM
Go to the first post in Chemicals and Chlorine ( this section ) and read the article on Bens Best Guess that should help you understand even better. The title gives you a clue to why I said that 30 to 50 PPM is the concensus. It is not hard science.
Good luck.
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