CYA and TA

[PoolInTheRain]

Two quick questions:

Can CYA level drop quickly, and if so, how?
-Upon opening, the CYA was only 5. We added using the sock method to get CYA to 40, and my own test and the pool store test verified the CYA level was in fact 40 (same results). I had the pool store run one because that's a tricky test to see well. However, I checked CYA yesterday it I could see the black dot when filling it all the way. The pool store's tester showed CYA at 40 again though.

What is my target TA?
-Poolmath says 50-90, with 60-80 being ideal, but I feel as though I've read here somewhere that I should be between 100 and 125?

 

[Texas Splash]

Since you had confirmation of a good (adjusted) CYA of 40 shortly after opening, it is odd that you are showing none on your test while the store showed 40. The R-0013 reagent is an inert substance that is generally very reliable. I would repeat the test carefully to confirm.

Your TA could be anywhere from 50 - 90. The 100 - 125 numbers sounds like pool store/industry quotes. But don't focus too much on a specific TA number. There is lots of flexibility with TA. As long as you are in that ballpark of 50-90 and the pH is stable by not rising too fast, it should be fine.

 

[PoolInTheRain]

Thanks, you are very helpful! I was wondering if the reagent wasn't good, so that clears that up. I was thinking maybe ammonia, but if I recall, my FC levels would be pretty much nothing with the presence of ammonia correct?

 

[Texas Splash]

Correct. When a pool gets ammonia, the CYA essentially becomes food and disappears very fast. You would not have received a CYA of 40 before. At the same time, the water eats-up chlorine exceptionally fast, so if you are able to record any FC at all, that also would rule-out ammonia.