Question about low CYA


Aug 5, 2021
Marin County, CA
Hi, I have seen that other people have asked similar questions, so I apologize if this is repetitive! As a new pool owner, I would love to get some thoughts on my specific situation. I had some leaky tiles that needed repairing. That required taking some water out of the pool. (It also meant leaving the pump off for 24hrs while the grout dried, which led to a minor algae bloom, but I took care of that). Now that we've replaced the missing water and the pool chemistry is back to normal, it appears the CYA level went down from around 35-40 to 20-25 because of the water replacement. My Taylor k-2006 test kit actually doesn't read that low, and I can see the black dot with the water right at the top, so I took it to a pool shop that actually uses Taylor kits. They have a test with a larger tube that can read lower ratings.

The chlorine seems to be holding well. Yesterday it was around 3.2 ppm in the morning, and I used the Poolmath app to raise it to 4 using 73% cal hypo (my calcium levels are on the low side, so I thought I'd use that, since i have a bucket of it that I bought before I knew anything and discovered this forum). This afternoon, it had only dropped to 3.2ppm. The water is clear. I just swam in it and I do feel like maybe the chlorine smell is a little bit more noticeable now, but that might be in my head.

Like others, I'm trying to figure out whether the low CYA is something I should care about. Does tend to just go up over time?

Here is my latest test result using the k-2006.
FC: 3.2
CC: 0
PH: 7.4
TA: 90
CH: 200
CYA: 20-25?
Temp: 84
CSI: -.30

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
Texas, San Antonio/Marion, South-Central Area
Pool Size
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
When you follow the TFP FC/CYA Chart, you do want a minimum CYA of at least 30. If you still receive hot sunlight and strong UV, perhaps 40-50 is even better. It's difficult to validate a CYA below 30 because the tube markings do not accommodate such low readings, so you want at least 30 or slightly higher.

A hint of chlorine smell is usually an indication of combined chlorines being oxidized, not the actual free chlorine. So be sure to maintain a good, healthy FC level as noted on that chart.
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