How to read TFT CYA Test

ontherocs

Active member
Mar 17, 2010
40
Tustin, CA (Orange County)
Hello,

Received my new TFTest Kit last week and finally was able to perform my own CYA test. The pool store had tested at 100. Before emptying and refilling, I wanted my own well measured test results.

When I first tested (Thursday) I felt comfortable with my results (80); but when I returned from vacation today (Wednesday) and retested, the results came in at 90.

Only acid has been added between those tests so I'm a little confused as to why the CYA would have gone up.

Wanted to ensure I understood how to read the results just in case the issue lies there. It seems like the test could be read differently depending on one's understanding and visual (20/20) limitations.

The instructions state: "Keep filling until the black dot in the bottom of the tube is completely obscured."

Does that mean that the black dot cannot be seen at all, not even a ghosting of it?

I also thought I read in some posts that temperature of the water and wiping the dropper bottles produces more accurate results.

Is that correct and can someone expand on the whys behind them if so?

THANKS!!!
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
See the photos in this link on the Taylor website. The black dot is completely obscured and there is no ghosting. The easiest thing to do is to add reagent until you think it might have disappeared, note that reading, add some more and see if it looks more obscured so you don't see the ghosting, then note that reading. It's like other tests where you add more until you don't see any more change. Then, pour from the tube back into the bottle and repeat the pouring into the tube. This way, you can go back and forth without having to use up more CYA reagent so can redo this disappearing act until you feel you've reached some sort of decent reading. With practice, you can narrow things down reasonably well.

You can get a Taylor R-7065-E 50 ppm CYA standard if you really are concerned about your readings, but this shouldn't be necessary.

As for viewing conditions, ideally you do the test outside with your back to the sun and your body shading the tube which you hold in front of you looking down into the tube. That is, there should be strong indirect light. If you measure in direct sunlight, your readings will be around 10 ppm too low. If you measure indoors without enough light, your readings will be 10 ppm or more too high.
 

mynewpool

Well-known member
Mar 17, 2010
1,082
Spring, TX
Out of all the test, this one is very hard to do. From reading on this site you can do the test over and over again with the same sample. Once you pour in the tube and get your results, pour back in the other bottle and do the test again. Maybe this will help you feel better about your results. I usually do this about 5 times and get the same results 3 out of the 5. Just takes practice and patience.
 

ontherocs

Active member
Mar 17, 2010
40
Tustin, CA (Orange County)
Thank you!!!!! I was looking all over for the example picts last night in the wrong place. :| Thanks for confirming that it needs to be completely gone. I'll also make sure to complete the test in strong indirect sunlight. I was testing under the patio shade. What? It was cooler under there! :) And a special thanks on reusing the solution to take a few readings!!!
 

mynewpool

Well-known member
Mar 17, 2010
1,082
Spring, TX
ontherocs said:
Thank you!!!!! I was looking all over for the example picts last night in the wrong place. :| Thanks for confirming that it needs to be completely gone. I'll also make sure to complete the test in strong indirect sunlight. I was testing under the patio shade. What? It was cooler under there! :) And a special thanks on reusing the solution to take a few readings!!!
Be careful when you are pouring it back in. Not that it will harm you, but not much room for error.
 
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