sudden loss of pool stabilizer

[norcalpool1]

All of last summer the pool had CYA of 60ppm. Solid stabilizer was added after the pool was replastered. The chlorine usage was around 1.5 ppm per day.

After rainy winter and pumping water out periodically, I noticed the CYA level had gone down to 30 at the start of summer. I added Natural Chemistry Liquid Stabilizer, 3 cups at a time. CYA level started going up and I stopped when the CYA level was at 50. I have the Taylor Standard 50-CYA solution and verified what I was looking for. I tested for CYA at least four times over a period of three weeks, when CYA was 50. Before that I tested the CYA every other day, to make sure CYA was increasing from 30 to 50 as I kept adding the liquid stabilizer.

Now here is what I don't understand. Within the last one week CYA level is back down to 30. How is that possible? Does the liquid stabilizer disintegrate quickly in hot days? Is the solid stabilizer chemically different from liquid stabilizer?

There has been just usual summer evaporation and addition of water. Nothing unusual with respect to the pool as far as I know. The big CYA loss happened in just 4 days.

There is some urban wildlife like raccoons, skunks, opossums and feral cats in the area, but there is no evidence of them ever going into the pool.

 

[frogabog]

There's been quite a lot of discussion lately about losing CYA in hot climates. I think I recall someone saying they're losing 10-15% perhaps monthly. Do some searching, try "CYA disappearing" and "losing CYA", or any other search strings you can think of. It's been said that CYA degrades some in hot climates.

It's news to me, I've been away for a few years and TFP has evolved in that time. Last I knew, CYA never went away without water changes. But now I read about it degrading with heat and everyone's talking about it (lots of southern pools here).

I'd trust your testing, it sounds like you're familiar with the test and know what you're doing. Probably add more CYA.

There's no difference between liquid and solid stabilizer. The liquid is simply the same stuff, dissolved in water and more expensive.

 

[Texas Splash]

Yeah, a CYA drop of about 30 in just 4 days is very strange. Assuming there is no water leak and we rule-out testing error or variance of 10-15%, then a good part of it may simply be that particular batch of stabilizer. We've seen over the years where some lots/batches of stabilizer seem to fail prematurely for no apparent reason. I had that problem with an HTH brand before, and it only seemed to be one bottle (granules). Weird. In the middle of summer, some pools hold their CYA well, while others may experience a 3-5 ppm drop from degregation, but that's about it. At this point all you can do is adjust and move forward.