Post-drain levels and suggested CYA supplement


Well-known member
Oct 30, 2018
Tucson, AZ
Performed a full drain and refill on my pool and spa. I thought I'd have some CYA left over residue, but it appears to be mostly gone. pH is a bit high as well, but easily treated with some MA. What is the best method to add some CYA?

Pre drain:
pH: 7.64
FC: 13 ppm
CH: 475 ppm
CYA: off the charts (>100 ppm)
TA: 110 ppm

Post drain:
pH: 8.49
FC: 0 ppm
CH: 200 ppm
CYA: None discernible
TA: 110 ppm


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Add the CYA by using what we call the sock method. Get an old sock (no holes) and put the measured amount of CYA you need. Tie the sock closed and either suspend it in front of a return (hang it from your brush pole works with something weighted on the deck) OR if it still allows flow thru the skimmer, place the sock in the skimmer. Every 15/20 minutes give the sock a squeeze to speed up the process. Please DO NOT follow the directions on the container of CYA to just pour it into the skimmer and don't just toss the sock in the pool as the CYA is acidic and can bleach/stain pool finishes.

I would suggest starting with enough CYA powder to add 30 ppm to your pool. Add enough MA to lower pH to 7.6 and liquid chlorine to get 3 ppm FC.