CYA very high?

Mar 23, 2017
Edmond, OK
Hi all, just opened pool to a green swamp. Have gotten water clear through use of chlorine tabs and shock (HTH 3 in 1). Last time I tested was at the pool store (I know, before I stumbled upon you guys), and it was I think 90 which was last week. We just had 3" of rain last night too and I haven't drained any off.

Here are my numbers today with a clear pool with just dead algae and dirt on the bottom. Zero green.

FC 6.0
CC 0.6
PH 7.2
TA 150
CH 800
CYA >100

Divin Dave

TFP Expert
LifeTime Supporter
Oct 2, 2013
Longview, Texas
Yeah, the CYA is way too high and most likely from use of shock and chlorine tabs over a period of time. When the shock and tabs add chlorine, they also add CYA. CYA doesn't go away on it's own. It just builds and builds with each tab. As the CYA level continues to increase, that means more chlorine needs to be added to be effective at keeping the pool sanitary. After a while, it becomes either impossible or unreasonable to add the amount of chlorine needed to overcome the buffering effects of the CYA.

Unfortunately, the only way to lower the CYA is to drain water from the pool and refill.

As for the rest of the test results - yeah, you know what Im gonna say about pool store testing don't ya! ? :)
If you intend on getting your CYA under control ASAP, don't worry about the rest of it until you do.


Mod Squad
LifeTime Supporter
Jan 17, 2012
Evans, Georgia
I would do the test again using equal parts pool water and tap water. Then use this water to perform the test again, but double the results. You may actually be well over 100+ on your CYA. That's gonna help you determine how much you need to drain and refill.

Yip :flower:

Oh yeah... and you need a better test kit than a pool store. Go for the TF-100 from Most comprehensive kit and will last all year and maybe into next...


Bronze Supporter
Feb 27, 2016
Danville, CA
It'll take time but you can deal with high CYA with partial draining /filling but have patience! Get rid of the pucks and use bleach only. Might take a year but use the chart to determine FC levels appropriate to your CYA number. It'll be fine, follow the program.