CYA Drift?

[Wobblerlorri]

I added 40 ppm CYA to my pool back in June when I first set it up. I test it once a month, because it was rock steady all through June, and one 16 oz bottle of reagent.

In July it was 40 ppm.

Tested it yesterday, it was 30. It tested for 30 very consistently. We did have a couple weeks of incredibly hot and bright weather. I also did two SLAMs during that time.

Now is this normal, or is it just the range of error?

Did I really burn off that much CYA in a month?

Did the two SLAMs in short succession burn off CYA?

Should I add more CYA to bring it back to 40 (5.4 oz per PoolMath)?

 

[mknauss]

CYA does degrade a small amount. With the testing accuracy of +/-10ppm to start with your tests are very realistic.

Add 10 ppm CYA

 

[Wobblerlorri]

Thanks Marty.

 

[Divin Dave]

Lorri,
You'll also loose some CYA due to overflow from rainfall. If you want your FC to last a little longer through August, then bring it back up to 40

 

[frogabog]

Backwashing & refilling? That's how I lost ~10ppm in three weeks. I expected it though. What I didn't expect was to be a moron and add 1c 6oz instead of 6oz which raised it by ~24-30ppm.