Cya question

mepcards

Well-known member
Sep 15, 2015
276
mesquite,tx
Last year I had the problem of my CYA too high, and the bleach was basically locked, and wasn't killing the algae, so I had to do partial drain. Now this year, im battling low CYA levels. A few weeks ago my CY level was at 30, so I raised it up to 50, but after testing this weekend, its back down and below 30. Now we still don't have a lot of evaporation due to its still winter, and of course no losing of water by splashing, for we cant swim yet. I have not had to replace much water, only if I do a good minute or two backwashing and rinse...Why does the CYA go down so quick? I get nervous about adding too much stabilizer, only to not have to run into that problem of partial drain again. My levels are below before adding stabilizer..

FC 12
CYA 25
PH 7.5
ALK 120

Vinyl ABOVE GROUD POOL
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,852
Tucson, AZ
How did you arrive at that value of 25ppm? The CYA test recommended in either the TF-100 kit or the K-2006 doesn't read that low very easily. Are you using the standard CYA test (R-0013) that comes with the test kit?


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domct203

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LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
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Last year I had the problem of my CYA too high, and the bleach was basically locked, and wasn't killing the algae, so I had to do partial drain. Now this year, im battling low CYA levels. A few weeks ago my CY level was at 30, so I raised it up to 50, but after testing this weekend, its back down and below 30. Now we still don't have a lot of evaporation due to its still winter, and of course no losing of water by splashing, for we cant swim yet. I have not had to replace much water, only if I do a good minute or two backwashing and rinse...Why does the CYA go down so quick? I get nervous about adding too much stabilizer, only to not have to run into that problem of partial drain again. My levels are below before adding stabilizer..

FC 12
CYA 25
PH 7.5
ALK 120

Vinyl ABOVE GROUD POOL
How are you getting these test results?

CYA doesn't evaporate with the water, and should not drop 20-30ppm in a few weeks unless you have exchanged about half of your pool water.
 

mepcards

Well-known member
Sep 15, 2015
276
mesquite,tx
The only reason im saying 25 is because I can still make out dot at 30, but when I add more just past the 30, then I cant see it, so im assuming in the 25 range..I had just purchased a brand new "big" bottle of R-0013...When I tested a few weeks ago it was 30, then I tested again after applying stabilizer, and it read 50...Two weeks later its below 30

- - - Updated - - -

I bought the big bottle on amazon. Hoping they didn't sell me fake reagent...It has all the labels on it....But have not replaced large amount of water, other than backwashing, and even when doing that, its only for a minute.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,852
Tucson, AZ
Well, it's always best to just round up. The test is only good to +/-15ppm and lighting conditions can very strongly affect the readings. I can read 80ppm when standing in full sun. If I take the same test sample and do the test under the shade of my awning, the reading drops by 20ppm and I read the exact same sample as 60ppm CYA. So test conditions are extremely important.

CYA only decreases for two reasons -

1. Water exchange (leak or overflow)
2. Slow oxidation by chlorine (~ 3-5ppm/month).

That's it. Other than testing error, there's no other way for the CYA to go lower.

As an aside - your TA seems to be a bit on the high side. But, if your pH is stable, then there's no reason to change it.


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domct203

Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
CT
Are you doing the CYA test outside on bright sunny days, with your back to the sun? Indoor lighting will yield unreliable results. Also, try not to block too much indirect light, try to hold the tube at the top with two fingers.
 

mepcards

Well-known member
Sep 15, 2015
276
mesquite,tx
Yes, testing outside with sun to my back..I also went by the chart for vinyl, and when it says Alk 90 + I assumed it was ok at 120...Even though my PH is good, should I still try and lower alk a little bit?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,852
Tucson, AZ
As long as your pH is stable and not falling or rising too fast, then it's fine.

As for the CYA test, you're at the low end of the test which is very hard to do. My suggestion is to not be so worried about CYA. A bleach pool can be easily operated with the CYA anywhere between 30-80ppm without problems. I have an SWG and I purposefully keep my CYA up at 90ppm and I have no troubles whatsoever. If you are manually dosing bleach, then that is what is typically the problem, not CYA. Manual bleach additions usually mean the FC is swinging around all day long (at first, high FC because of the bleach and then too low because bleach wasn't added soon enough).

So I would add 10ppm CYA (easiest way to do that is with pucks in a floater) and then retest. Keep doing that until you see your CYA get up near 40-50ppm and then stop. Then just go with bleach. If your CYA drops rapidly again, then start looking for leaks or considering if overflow is an issue.


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mepcards

Well-known member
Sep 15, 2015
276
mesquite,tx
Ok...well I do have a big bucket of pucks ive never used last year after adopting the BBB method..I can say for sure no overflow, for we havnt had any rain that heavy to fill pool to the top. Also I think im good with no leaks, for my water level has stayed very consistent thru out the winter, barring the fact to raise it a inch at the most, but nothing major to where im like dang, im having to add water a lot, and its not even hot enough to evaporate. Im going to run test again, and make sure I didn't also get some bad regeant from amazon..
 

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