CYA question


Well-known member
May 18, 2010
I'm sure this is going to be a "duh" question but here goes...

My CYA has been testing consistently at 80 for a month (TF-100 kit). A few days ago I tested CYA and it was 90. I haven't added any CYA, so my assumption is I just performed a bad test and should just test again, right? It can't go up without adding!


TFP Expert
LifeTime Supporter
Feb 23, 2008
Denton, TX
It won't go up unless you added some. You can get some variance on the test because there is so much left to personal interpretation. Even changing the time of day that you test it can make it look different due to the difference in available light.


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
The CYA test is not especially precise. Two CYA measurements within 10 of each other might as well be the same.


TFP Expert
LifeTime Supporter
Apr 4, 2009
Absolutely agree...the other cause could be that perhaps you had some evaporation since your last CYA your CYA concentration may be slightly higher...although if you have an autofil, you can throw that theory out the window :lol:

Anyways, I always view the CYA test as a +/-10ppm measure...cracks me up when someone reports CYA of lets say 47 :hammer: ...I get all cross eyed :shock: everytime I do that test, staring at that darn dot. :roll:

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