CYA reagent not working?

forfarmforfam

Member
May 7, 2013
5
Hello,
First of all, THANK YOU for your site. I began by reading everything I could from your site years ago. We finally realized we didn't need to do anything but keep chlorine added to the pool on a fairly regular basis, and our pool water stayed clear and clean looking.
Now I write because I decided to check everything over with a TF-100 kit (years old) before we put a cover on the pool, and found things might not be as balanced as I thought. Mainly I wonder if the cya reagent is not working. I began by checking the FC and pH before adding chlorine in order to shock. That began the journey to figure out how much chlorine I needed to shock. The FC first registered - none. So, I tested the CYA. The black dot never disappeared. It got smaller, but was still visible. So, I decided to just throw a bunch of chlorine in and see what was left in the morning. 3.5 gallons of 7.55%. There was a lot of chlorine in the morning. Waited till the afternoon on this very sunny day. Still registers at 20ppm. Here are the rest of the numbers:
FC 20
CC - forget because I was interrupted. Couldn't remember if I had dropped the reagent in, but thought I had. However, it was pink
again. I didn't want to use all of the chemicals, again, so I just dropped 3 more drops in, and it turned clear.
TA 100 (blue to yellow, rather than green to red - supporting lots of chlorine is still in there)
pH - above 8.2
CYA - smaller dot, but still visible when tube was completely filled. But with the chlorine lasting so well... maybe the reagent isn't still good?
Although we are in Indian Summer, I don't know that we have many more days to adjust anything. Should I just cover the pool and start over in the spring with a new kit, and working to bring the pH down?

THANK YOU!!!! for being there!!!!
 

Rocket J Squirrel

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Your reagents are "years old"? How many years? The CYA reagent is pretty stable, but nothing lasts forever. You can get a complete refill set of reagents from tftestkits.net.
 

bmoreswim

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You should let the water warm up to 70 degrees before testing CYA. Cold water affects that test. Not sure what your water temp is but if you are putting the cover on soon it is probably cooler than it should be for testing.

And yes, getting fresh reagents is always wise. It is an unknown if using old reagents
 

mgtfp

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Mar 5, 2020
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I remember a post from Chem Geek where he mentioned that at high FC, the CYA that is bound to chlorine might not react with the CYA test reagent. Try adding a few drops of R-0007 to dechlorinate the sample first. And make sure that the sample is at least at room temperature before testing as mentioned above.

EDIT: Found the post:

A high FC, on the other hand, can have most of the chlorine bound to the CYA and that can interfere with that combination from forming melaminecyanurate (details in this post). So I would NOT say that high FC does not affect the CYA test -- it might, though it would result in a lower than expected CYA reading, not higher. So if you want to test CYA at higher than normal FC levels (say, 10 ppm FC or higher) you could use sodium thiosulfate solution (R-0007) or hydrogen peroxide to dechlorinate the sample first. We normally have people test CYA at normal FC levels before a SLAM so this issue usually does not come up.
 
Last edited:

forfarmforfam

Member
May 7, 2013
5
Thank you, very much! Those answers helped a lot. I will retest after the water warms. And, of course, I will order a refill kit at the beginning of next season. Thanks, again!
 
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