CYA test


Silver Supporter
Aug 28, 2012
Houston, TX
Hello to All,

I Know the CYA test is the most subjective of all. However, wanted to run a few things by you guys:

1. When pouring in the solution to "block-out" the dot, what's the best way:

a. outside in sun?
b. outside when cloudy or under a covered roof?
c.. inside under a light?
d. inside using natural light
e. other?

2. I'm 6'4", so when it says hold tube by your side, I would say the reading w someone 5'4" is going to be diff. Is there any rule on making adjustments for this?

Thanks, tstex

PS - my last CYA went all the way to the top and I still saw the dot - I do believe, however, that the CYA had been highly diluted w lots of rain and all 8.25% bleach, but not a bad thing during winter for the FC - thanks again
Mar 24, 2014
Greenville, SC
1. Outside, in full sun with your back to the sun.

2. Hold it at your belt buckle. That's close enough for rock and roll, even for the tallest.

3 :) Squirt, glance, repeat. Don't stare at the dot. When you think the dot disappears, pour it back in the squirt bottle and do it again. Do it 2-3 times and average what you get.

e: 3b Pinch the top with 2 fingers, don't wrap your hand around the tube. You want as much ambient light into the tube as possible.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Another simple trick is to go "digital" - just fill the tube up to the 100ppm mark. Can you still see the dot? Yes, then fill it up to the 90ppm mark. Can you still see the dot? Yes, then fill it up to the 80ppm mark. IS the dot still there? etc, etc, etc. TFP recommendations only matter to within 10ppm for CYA AND the test is only good to +/- 15ppm CYA so there's no point in trying to find the exact point at which the dot disappears...And, by turning you eyes away to fill up the tube each time, you avoid the problem of intentional staring which can make you "see" the dot even when it is not there....


Silver Supporter
Aug 28, 2012
Houston, TX
Bruce & Matt,

Thanks, just what the Dr ordered - going to transfer info to my pool testing notes.

As suspected, I was under the assumption a suggestion test would indeed have a larger std deviation, but might as well do it as correct and precise as possible. I'm going to let me last acid additions take full impact and will post all my reading tomorrow am.

Thanks again, tstex