How do I reduce my CYA levels?

[aces79]

I have a 30x52 above ground chlorine pool. I have a TF-100 test kit.

My CYA showed 120 so I let half my water out, refilled it, let the pump run for 24 hours and retested. My CYA was 95.

I repeated the process and my CYA is now at 70.


Why didn’t it reduce by half each time I drained it?

If I empty it again to get it closer to 40/50, how much should I empty?

Also, I use chlorine tabs in my online chlorination. This also raises the CYA level, correct? So how do I prevent that?

 

[mas985]

Replacing half the water should have reduced the CYA by half unless it is sitting somewhere and not fully dissolved. Did the water level actually drop to half the height (~2')? Are you rinsing out the test tube between tests? There can be some error in testing as well.

 

[mknauss]

Did you test the CYA of 120 and 95 using the dilute method?

If you are at 70 now, and your pool is 48" deep (typical of an above ground pool), drain 20 " and refill.

You will then chlorinate with liquid chlorine. Adding what is needed based on testing, every day.