CYA / Trichlor Math

Jeff J.

Active member
Aug 6, 2019
Staten Island NY
I'm trying to understand the math of CYA buildup. I've read that one 3 inch puck adds about 3.3 CYA per 10k. But I've also read recently that CYA degrades at about 5.0 per month. Where I am, we have about a three month season. So if I put in 2 pucks a week, it would add roughly 78 CYA to my 11k pool. But the pool will lose about 60 during the year, not counting splashout and the partial drain for closing. Is that right? I use liquid now, but if I could keep a puck or two in the floater to supplement without too much CYA buildup, it would be a little easier.


Gold Supporter
Jun 28, 2017
Fresno, CA
The degradation rate for CYA is a wild guess and making assumptions on this is unreliable.
I am hoping you have a good test kit and can properly test your pool water chemistry. This relationship is critical FC/CYA Chart
Estimating your CYA additions using Pool Math PoolMath will help you arrive at a good plan.
Many people here manage their pool systems using liquid Chlorine and supplement with pucks to to maintain CYA, pH and FC during days away from home.
Good sanitation plans start with proper water testing, understanding your pool system and your chemical additions.
  • Like
Reactions: Jeff J.


Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
Tucson, AZ
:wave: Welcome to TFP!!!

The CYA degradation is not a fixed 5ppm / month ... it is highly variable depending on water temperature, sun exposure, and FC levels.

Your environment (short season, rain, etc) makes the possibility of being successful with trichlor puck use pretty good, as long as you are still using the proper test kit and monitoring your levels, ensuring that the FC does not drop too low for the CYA level and supplementing with bleach as required.
  • Like
Reactions: Jeff J.