Water Exchange/CYA Question


Well-known member
Jun 8, 2013
East Texas
Over the past 24 hours I have replaced about 12 inches of water in my pool (not sure how else to give a measurement). Pool is full and as expected all levels are now off. I read where to get my CYA in check then rebalance, correct? My question is - Does the CYA drop over time with the water exchange or will a test be accurate soon as pool is refilled?
This afternoon's results:
FC - waiting on FAS-DPD but still registers some FC
pH - 7.4
TA - 140
CH - 160
CYA - 140-150 (two test, using dilution method)

I feel like I am missing something? Keep draining?


Gold Supporter
Bronze Supporter
Jun 11, 2018
Verona, MO
Any idea on average depth? For example average depth 5' = 60". Divide 12 by 60 =.2 or 20%. Unless my math is wrong, I think to get to 60cya you will need about 60%, almost 80% to get to 40.

Draining in 12" increments and replacing will require an even larger replacement due to dilution as you go.

I guess my point being nailing down CYA after the first 12" exchange doesn't need to be super accurate.

Good Luck on your mission!