My test, where did the CYA go?

[boston2austin]

I chlorinate with bleach, not trichlor. My CYA has run about 40 all summer. Today I test it (new reagent) and find it to be almost undetectable. I went to the Pool Store to verify, and they confirm

Another barely related question: I have done some of the reading on the loss of strength over time of chlorine. Is that a measurable loss or just an effective loss. That is, if you use old, weak bleach, will the FC reflect that or will it still rise with the addition of that weak bleach. Considering that in relation to my trichlor, will it be effective or just trash it?

Results mine theirs
FC 4.5 5
CC 0.5 0 (according to my tests, I can almost NEVER get this to zero even while shocking)
pH 7.8 6.8 (Added MA before taking store sample and not enough time to mix)
TA 60 50
CH 270 150
CYA <20 20
T 76 degrees

Where did the CYA go? Had some rain recently, but not too much. I don't backwash.

Moving forward, should I just start using the trichlor that has been on my patio for the past 4 months, use stabilizer, or the "conditioner" they wanted to sell me.
Any feedback?

 

[Stuamurr]

I think I remember reading something about Cyanuric Acid degradation before, but I am just surmising, someone with knowledge of that can speculate better on your CYA level dropping.

As for increasing your CYA I would go with option 1 and use your Tri-Tabs.

Sodium Hypochlorite does lose strength over time, however is still usable, you will notice the amount of Free Chlorine you receive is less than a fresh jug, but there's no reason not to use it.

 

[UnderWaterVanya]

Weak bleach will give less FC than normal. FC of a given number is there the same no matter what it started out as.

-sent with Tapatalk 2

 

[chem geek]

CYA slowly degrades from chlorine, but at around 2-3 ppm per month so not usually noticeable except over a season. There might be some faster oxidation of CYA that we don't yet understand -- we know it can happen when the FC gets to zero and the CYA gets consumed by bacteria, but during the summer keeping the FC up that shouldn't happen. The rain could have diluted it some, but probably not by a lot and your other parameters such as CH should have been affected by such dilution as well (though CH can also increase from evaporation and refill with water that has CH).

 

[kimkats]

Interesting you should post this. I was going to do a search on losing CYA. I have not been able to keep my CYA up. Two weeks ago I got it up to 40. I tested it yesterday and it was back down to 25! This is a very low use pool. Two adults that love to float and enjoy. Well husband does love to jump in and splash me but.........that is only every once in a while.

Everything else is sitting pretty!

I will be buying more balancer this afternoon to add. I was SO worried about having high CYA LOL Guess that is not a problem!

Kim

 

[dmanb2b]

Interesting you should post this. I was going to do a search on losing CYA. I have not been able to keep my CYA up. Two weeks ago I got it up to 40. I tested it yesterday and it was back down to 25! This is a very low use pool. Two adults that love to float and enjoy. Well husband does love to jump in and splash me but.........that is only every once in a while.

Everything else is sitting pretty!

I will be buying more balancer this afternoon to add. I was SO worried about having high CYA LOL Guess that is not a problem!

Kim

Thats a rapid decline, but strong rains (FL) will dilute CYA levels some. Remeber the CYA test is accurate to within +/-10ppm, so it could also be your result off by 10ppm and the added effect of dilution.

 

[Mona]

Interesting you should post this. I was going to do a search on losing CYA. I have not been able to keep my CYA up. Two weeks ago I got it up to 40. I tested it yesterday and it was back down to 25! This is a very low use pool. Two adults that love to float and enjoy. Well husband does love to jump in and splash me but.........that is only every once in a while.

Everything else is sitting pretty!

I will be buying more balancer this afternoon to add. I was SO worried about having high CYA LOL Guess that is not a problem!

Kim

Are you testing the same time of day, in the same sunlight/shade? It should not vary like that without something going on.
I know here (I'm in SE Minnesota) I lose some CYA over the winter, but not during the summer when the pool is open and levels maintained.

 

[kimkats]

I have been VERY careful to test at the same time of day, in the same place, etc. for CYA.

I did not even think about the RAIN! We had a HUGE rain event last week where we had to drain some water out-DUH!!!

Thanks for reminding me about the rain/drain!

Kim