CYA lowered unexpectedly

[Comeby]

Moved from here.
I’m running into something weird. I had cya at about 40-50. Had to go out of town for an extended period so I added lots of liquid chlorine and dropped a few tabs in the inline, knowing it’ll bump my CYA. Did this twice got two trips. Checked CYA when I got back= 0. Figured it was old Chems so I ordered a new set for Cya, checked again, same result. I don’t see any leaks or running water or anything to sewer. I’m also having to fight the chlorine monster more often. There for a bit adding a gallon of 10% every 2 days.

 

[TexEdmond]

That definitely is weird. The only two ways I'm aware to drop CYA to zero are: 1.) Drain 100% of pool water and refill, and 2.) a certain bacteria grows in the pool after extended periods of 0ppmFC and the bacteria eats the CYA. Did your CYA fall to 0 during your trip? Did the pool go green and get foamy on the top?

 

[Mdragger88]

I’m running into something weird. I had cya at about 40-50. Had to go out of town for an extended period so I added lots of liquid chlorine and dropped a few tabs in the inline, knowing it’ll bump my CYA. Did this twice got two trips. Checked CYA when I got back= 0. Figured it was old Chems so I ordered a new set for Cya, checked again, same result. I don’t see any leaks or running water or anything to sewer. I’m also having to fight the chlorine monster more often. There for a bit adding a gallon of 10% every 2 days.

Cya may be just below 20 - so unmeasurable. Which is not that far below 40 & a reasonable loss depending upon the heat, rain, backwashing,& length of time since you last checked.
Add 10-20 ppm via the sock method & re check in 24 hrs.
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[Comeby]

That definitely is weird. The only two ways I'm aware to drop CYA to zero are: 1.) Drain 100% of pool water and refill, and 2.) a certain bacteria grows in the pool after extended periods of 0ppmFC and the bacteria eats the CYA. Did your CYA fall to 0 during your trip? Did the pool go green and get foamy on the top?

That’s why I’m wondering if I just have a bad batch or reactant. No foam but I am having trouble keeping FC levels up. There’s an algae that looks like green pollen that keeps coming up in shallow spots and on the ledge and steps. It’s easy to brush.
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