CYA loss question. Again!!!


Bronze Supporter
Dec 13, 2018
Orlando, FL
At the beginning of the year, my CYA was 60ppm. I have been struggling all year to get my CYA up. It seems to always drift down to 50ppm.

So since the beginning of the year (Jan), I have added 131 Oz. of CYA (sometimes in sock in skimmer basket and sometimes in sock hanging in front of a return). This should have raised CYA to 128 ppm (per Pool Math). Assuming I am losing 5 ppm per month, my CYA should be about 108. However, it is still between 50-60ppm.

I ordered the CYA calibration standard and I am seeing the dot disappear at 50ppm and testing in same conditions, so I feel good about the test results.

I added another 12.8 oz. tonight (all I had on hand), which should put me over 60ppm.

I have a lot of evaporation due to heated water and splash over bowls, but I should not be losing CYA due to evaporation. I did a bucket test a few times and did not see any significant difference in pool water vs. bucket water.

One theory I have is that I am possibly cleaning the filter too soon after adding the CYA. So this time I cleaned filter first and then added CYA (in sock in skimmer basket). I should not have to clean for at least 2 weeks or more. Just came off a SLAM and everything is pretty clean.

Another theory is that the CYA is bad. I bought some from Lowe's and some from Home Depot.

My question is, where is it going?

P.S. My PoolMath logs are not fully back logged yet. I am still inputting information from my spreadsheet to the app. I'm only back to beginning of month.


Bronze Supporter
Dec 13, 2018
Orlando, FL
Do you have an autofill?

Do you have an overflow drain?

What temperature is your pool?

No auto fill.

No overflow.


Thanks for the article. I have read that. I forgot it can go as high as 10ppm loss.

I do face south and have full sun all day, even in winter. But we have a screen, so that should cut down some I would think

Let’s assume I added enough to get to 128ppm. I’ll round down to 120ppm. Then losing 10ppm per month gets me to 80ppm. Then assume some loss due to filter cleaning and test error. That gets me to the 50-60ppm I am now.

Feasible? Or gross conceptual error?


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
The CYA test is imprecise enough that your testing can be off by +/- 10 ppm.

Keep on testing your CYA at least evert 2 weeks and track in PM the trends and stabilizer additions.