Last night CYA was down to 20

[steelman93]

Moved to a new topic. If there is any chance of hijacking, please start a new topic. JasonLion

Sorry to hijack the thread, but I was going to post the exact same question. I am using the TF test kit in a 19,000 SWG inground, vinyl pool. I added 4 pounds of stabilizer at the beginning of the year per the pool store recommendations then, through a miscommunication my son added another 4 pounds. After that i switched to doing my on tests using the TF kit. At the end of May my CYA was 30, and stayed there for the next 2 weeks, testing once a week. last night it was down to 20. What happens to the CYA? I have lost about 4-6 inches of water through evaporation (warm sunny days, cold nights here in VA. I use a solar heater which raises the temp 10 degrees during the day) So if I don't have a leak and I don't backwash because I have a cartridge and I have not added water, what happened to the CYA? Is it possible the test is not accurate?

I have also noticed a drop in TA from 130 to 90 over the same period. I used to use the local pool store(s) for testing but got frustrated with contradictory results so I bought the test kit and am now trying to understand chemistry.

Thanks for opinions.

 

[JasonLion]

The CYA test is accurate, but not precise. It is accurately telling you that your CYA level is somewhere around 20 or 30, but not exactly where. The precision of the test is +-15, so those results are consistent with each other and with the level not actually changing.