Recommended CYA level for hot tub - test kit can't measure below 30ppm

Sep 1, 2021
Pool Size
Liquid Chlorine
Looking through the 'how to use chlorine in hot tub' article, it suggests that CYA be between 20-50ppm. Based on the amount of Dichlor I've used so far, my CYA should be about 22ppm (based on PoolMath app). The minimum that the CYA test in my K-2006C kit can measure is 30ppm, the water is noticeably cloudier than when I tested after a fresh fill, but the dot is still visible with the vial all the way full. So all I can say for sure is that I'm under 30ppm CYA.

Should I use Dichlor until the dot disappears with a full vial (so ~30ppm), then use bleach until the dot is visible again? I'm assuming the CYA will slowly degrade/offgass/etc due to the heated water or some exposure to sunlight. Or does that take so long that I'll be draining the water for other reasons before the CYA would come down?


Gold Supporter
Feb 24, 2015
Santa Cruz, CA
I shoot for 30ppm to start and test for it to verify - then after a few weeks I test again (expecting it to have dropped) - if it has dropped I add around 20ppm worth which typically gets me back to the 30ish range.