Where did my CYA go?

[Deb04]

When we opened the pool in May, the CYA was 20. It always drops significantly over the winter. Started adding and testing CYA and got it to 70 about a month ago. (BTW, just for giggles, I also had a Pool Store test, and they said 85.) I hadn't tested CYA since.

Today is hot and very pregnant daughter and her husband are coming over to swim. I, of course, want the water perfect for her and my soon to be born Grandbaby.

FC = 8.5
CC = 0
pH = 7.4
CYA: The little dot still was a little visible at the top of the tube.

What? Where'd my CYA go?http://www.troublefreepool.com/images/smilies/confused.png

We had lots of rain over the past few days and we got maybe 2-3 inches more water in the pool. We didn't drain any. I can see how that would dilute the CYA. But it's a 19K gallon pool. I wouldn't think it would go down to < 20.

Thoughts?

 

[JasonLion]

Small changes in CYA can be the result of testing problems. But large CYA changes are either water replacement, or (very uncommon) periods when the FC level went to zero and bacteria ate the CYA.

Any chance you have an autofill system and a slow water leak?

 

[Deb04]

We don't have an autofill system. I'm going to test again. I tested twice this morning, but with the same mixture. I'll try mixing again.

I test the FC every day, so I know it didn't go to zero.

 

[Deb04]

Tested twice more with a new mixture. This time I got 30.