Confusing why CYA is too high

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sjsoldo

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Jul 17, 2009
105
25,000 gal pool with SWG. During the winter I turn off the SWG and add a few pucks a month to the water via a floating dispenser. I have not added CYA to the pool over the last four years.

I add about 1/2 gallon of acid a week to keep proper pH.

In the summer, about every 7-10 days I add 3 bags of "sodium dichloro-s-triazinetrione" powder. (Yes I know you guys discourage powder shock, but it does work). I also add some phosphate lowering product (I know you hate that too) in the spring. Finally, I do add a small amount of bromine ("No-More problems") every few months. All of this will usually keep yellow algae out of my pool.

So this week I tested the CYA level and it is greater than 100 !!! Tested it again, made sure it was mixed properly and got the same results. I am using the Taylor test kit where you add the mixture (7 ml pool water+7 ml of reagent) until you cannot see the black dot anymore.

What is happening???
 
It's really not too confusing. Remember, CYA is added to the pool either by stabilized chlorine products or CYA on its own. Each puck you use and every bag of "shock" (in your case, dichlor) adds to it.

The only "shock" you should be using is bleach.

Here some good info from Pool School.

The bleach alternatives are not necessarily bad, as long as you know that the side effects are intentional on your part.
 
3 bags of dichlor in your pool will add about 7.3 ppm of CYA. If you add 3 pounds per week, then in 14 weeks, your CYA will be raised by 100 ppm.

Sodium bromide has turned your pool into a bromine pool, which will cause you to lose most of your chlorine as fast as it can be made by your SWG.

You really need to read pool school as some of what you are doing is counterproductive and causing you problems.

Used correctly, a SWG will pretty much do everything you need. If you need to add anything other than minor amounts of salt and CYA to make up for dilution, then you are not doing it the best possible way.
 
The following are chemical facts independent of concentration of product or of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.
 
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