CYA Mystery

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PoolYaYa

PoolYaYa

Member
Jun 8, 2021
8
Redlands, California
Pool Size
23000
Chlorine
Liquid Chlorine
My CYA has stayed steady for months—at 35. I test regularly with a Taylor Kit and at our pool store to confirm numbers. We use liquid chlorine only. A few weeks ago I placed the solar cover on anticipating the swim season. We also fired up the heater after a few days. I continued to test chlorine levels—and all was well at a steady 3-4 ppm. All other numbers were within normal range. Then we went on a short 4 day trip. When we came home I immediately tested the water and chlorine was at 0 and the CYA was at 5!!!!! Huh? Took a sample to the pool store and they couldn’t believe what they were seeing. CYA dropped 30 ppm in 2 weeks. We didn’t replace water. No one can explain this mystery. I checked the internet and this seems to be unique. Could the solar cover or rapid heat increase have created some kind of chemical change?
(We removed cover and added CYA. Everything is back to normal, but I’m afraid to put the solar cover back on!!! Yikes!) Can you reassure me this won’t happen again???
 
There is a CYA eating bacteria. It's not that uncommon. Check your water for ammonia that's a tell tale marker. Can you hold chlorine? If so then the ammonia is most likely gone already. Your CYA was low to begin with though.
 
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PoolYaYa said:
My CYA has stayed steady for months—at 35. I test regularly with a Taylor Kit and at our pool store to confirm numbers. We use liquid chlorine only. A few weeks ago I placed the solar cover on anticipating the swim season. We also fired up the heater after a few days. I continued to test chlorine levels—and all was well at a steady 3-4 ppm. All other numbers were within normal range. Then we went on a short 4 day trip. When we came home I immediately tested the water and chlorine was at 0 and the CYA was at 5!!!!! Huh? Took a sample to the pool store and they couldn’t believe what they were seeing. CYA dropped 30 ppm in 2 weeks. We didn’t replace water. No one can explain this mystery. I checked the internet and this seems to be unique. Could the solar cover or rapid heat increase have created some kind of chemical change?
(We removed cover and added CYA. Everything is back to normal, but I’m afraid to put the solar cover back on!!! Yikes!) Can you reassure me this won’t happen again???
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Don’t trust the pool store CYA test (or any of their tests for that matter).

If the cover has algae on it, that can consume chlorine very fast.
 
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How did you test a 5 CYA before going to the pool store to confirm ? The Taylor tests start at 20 or 30 depending on the model. Anything below that is sketchy at best to try and read.

The CYA test is arguably the pool stores least accurate test so that's sketchy result # 2.
 
PoolGate said:
There is a CYA eating bacteria. It's not that uncommon. Check your water for ammonia that's a tell tale marker. Can you hold chlorine? If so then the ammonia is most likely gone already. Your CYA was low to begin with though.
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I did read that. I’m holding chlorine fine now. Could the solar cover have caused an ammonia trap?
CYA should be at 30-50, correct?
 
PoolYaYa said:
Could the solar cover have caused an ammonia trap?
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You likely would have known it was ammonia. It takes lots of chlorine to kill ammonia. Lots and lots even. You wouldn't have cleared it with a regular dose or two after returning from the trip.

Then it would have converted the CYA you added to more ammonia and you'd be staring down quite the battle right now.
 
The first step to a trouble free pool is to start doing your own tests with a high quality test kit like one from Taylor and stop going to pool stores for any reason.
 
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Newdude said:
You likely would have known it was ammonia. It takes lots of chlorine to kill ammonia. Lots and lots even. You wouldn't have cleared it with a regular dose or two after returning from the trip.

Then it would have converted the CYA you added to more ammonia and you'd be staring down quite the battle right now.
Click to expand...
Very good to know!!!!
 
PoolGate said:
The first step to a trouble free pool is to start doing your own tests with a high quality test kit like one from Taylor and stop going to pool stores for any reason.
Click to expand...
My Taylor kit tests and my pool store tests agree 100%. Totally trustworthy store. I went to confirm my CYA test because to lose 30 ppm in 2 weeks is almost unheard of. So before I added stabilizer, I confirmed.
Respectfully, what would you have done? Thank you for your expertise on why this happened.
 
PoolYaYa said:
My Taylor kit tests and my pool store tests agree 100%. Totally trustworthy store. I went to confirm my CYA test because to lose 30 ppm in 2 weeks is almost unheard of. So before I added stabilizer, I confirmed.
Respectfully, what would you have done? Thank you for your expertise on why this happened.
Click to expand...

I do weekly tests so my CYA never would have gotten that low. 😉 But in reality, testing that low of an amount isn't very accurate. The testing scale for CYA is logarithmic not linear. When you get down to just a few parts it's close to zero. I doubt you lost any significant CYA over the normal degradation it just appeared so because you didn't have much to begin with.
 
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PoolYaYa said:
because to lose 30 ppm in 2 weeks is almost unheard of.
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Again. Testing at 20 and below is sketchy at best, so really that means testing under 30 is sketchy at best. Unless it's 0 CYA from fill, we reccomend adding 10 or 15 at a time, allowing plenty of time to mix until it registers at 30.

PoolYaYa said:
Why do you think this loss happened?
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CYA degrades 3 to 5 ppm a month, and maybe a little more in the hot climates. It most likely had degraded a little but not really registered on the test. Then when it degraded a little more it registered a bigger loss than actually happened.
 
PoolYaYa said:
My Taylor kit tests and my pool store tests agree 100%. Totally trustworthy store. I went to confirm my CYA test because to lose 30 ppm in 2 weeks is almost unheard of. So before I added stabilizer, I confirmed.
Respectfully, what would you have done? Thank you for your expertise on why this happened.
Click to expand...
I think I would have added 15ppm or so, maybe 20. But if you added 30 and it even as high as 20 you’d be at 50 which isn’t bad. What is the cya measuring now?

I actually had the ammonia cycle to deal with this year. What a pain.
 
Newdude said:
How did you test a 5 CYA before going to the pool store to confirm ? The Taylor tests start at 20 or 30 depending on the model. Anything below that is sketchy at best to try and read.

The CYA test is arguably the pool stores least accurate test so that's sketchy result # 2.
Click to expand...
You are correct! The dot was still showing ALL the way up past 30 (brand new reagent). So I assumed it was lower than 30. Then I went to the store whose tests always match my Taylor kit numbers to find the actual CYA number. They tested it twice at 5. (And they tested it at 44 yesterday and I tested it at 40, so I feel they are accurate.)
UnderWaterVanya said:
I think I would have added 15ppm or so, maybe 20. But if you added 30 and it even as high as 20 you’d be at 50 which isn’t bad. What is the cya measuring now?

I actually had the ammonia cycle to deal with this year. What a pain.
Click to expand...
It’s at 44 ppm.
Mdragger88 said:
So you are passing an
Overnight Chlorine Loss Test?
As mentioned you can’t read under 20ppm cya reliably so add 10-20 ppm worth via the sock method & retest in a day.
& scrub that cover!
Click to expand...
What do I scrub it with?
 
Newdude said:
Again. Testing at 20 and below is sketchy at best, so really that means testing under 30 is sketchy at best. Unless it's 0 CYA from fill, we reccomend adding 10 or 15 at a time, allowing plenty of time to mix until it registers at 30.


CYA degrades 3 to 5 ppm a month, and maybe a little more in the hot climates. It most likely had degraded a little but not really registered on the test. Then when it degraded a little more it registered a bigger loss than actually happened.
Click to expand...
Ok, that makes sense. In 4 yrs I’ve never seen that happen so quickly though.
 
PoolYaYa said:
You are correct! The dot was still showing ALL the way up past 30 (brand new reagent). So I assumed it was lower than 30. Then I went to the store whose tests always match my Taylor kit numbers to find the actual CYA number. They tested it twice at 5. (And they tested it at 44 yesterday and I tested it at 40, so I feel they are accurate.)

It’s at 44 ppm.

What do I scrub it with?
Click to expand...
Diluted bleach & water & pool brush.
Anywhere between 40 & 50 counts as 50.
 
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