cya level in pool dropping

Bozer4

Active member
Jul 11, 2019
34
Manteca ca
Hello, My CYA level in my pool dropped from 40ppm to 35ppm over a 3 week period, is this normal? It has been hot out here, averaging between 95 and 105 degrees for multiple weeks, so I'm sure there's a lot of evaporation. I'm using liquid instant conditioner by Natural Chemistry. It's been a consistent loss, I've lost 10ppm over 6 weeks.
Thanks, Brett
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,848
Northern NJ
40 CYA vs 35 CYA (which is not a valid reading that you cannot measures) is with in normal testing variation.

CYA is not lost in water evaporation. CYA does degrade by chlorine and high water temperature.

Losing 10 ppm in 6 weeks is not something to be concerned about. Just add 10 ppm of stabilizer.
 

Bozer4

Active member
Jul 11, 2019
34
Manteca ca
You're right, sometimes differentiating between 40 CYA vs 35 CYA can be difficult because of the disappearing black dot with the CYA test. I wish they had a test for CYA that had color changes like all the other tests. My pool temp has been between 80-85 degrees and free chlorine 5-7 so I guess that's where I'm getting the degradation of CYA. Thanks for the advise, I'll add 10 ppm of liquid instant conditioner and call it good.
Brett
 

Bozer4

Active member
Jul 11, 2019
34
Manteca ca
I forgot to mention that my pool has an automatic pool refill system. I understand that CYA is not lost in water evaporation but wouldn't CYA level drop due to city water replenishment from pool refill system?
Brett
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
23,066
Laughlin, NV
I forgot to mention that my pool has an automatic pool refill system. I understand that CYA is not lost in water evaporation but wouldn't CYA level drop due to city water replenishment from pool refill system?
Brett
No. Unless it is refilling due to you draining water from the pool.

There is natural degradation of CYA in water primarily due to elevated water temperatures.
 
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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,848
Northern NJ
As water evaporates the CYA level in the remaining water rises. CYA stay behind when water evaporates. Then when you add water to refill the CYA level returns to what it was.
 

Jason245

Well-known member
Jul 27, 2019
72
Fort Lauderdale FL
40 CYA vs 35 CYA (which is not a valid reading that you cannot measures) is with in normal testing variation.

CYA is not lost in water evaporation. CYA does degrade by chlorine and high water temperature.

Losing 10 ppm in 6 weeks is not something to be concerned about. Just add 10 ppm of stabilizer.

Wow.. and I thought I was crazy when I started seeing my CYA drop.

So basically I will lose about 10PPM CYA a month with ~80-85 degree water?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,848
Northern NJ
Wow.. and I thought I was crazy when I started seeing my CYA drop.

So basically I will lose about 10PPM CYA a month with ~80-85 degree water?
Chem Geek discussed the various ways CYA degrades in this thread ...

 

Jason245

Well-known member
Jul 27, 2019
72
Fort Lauderdale FL
Just take our word for it then.

I have been taking the word of people on here like it is the gospel of pool science... if you told me that on the 12th day of the 12th hour of the 12th minute of the 12th second of the 12th month if the moon is full, all the water magically moves from the shallow end to the deep end creating a tsunami... I would probably make sure everyone was out of the pool and wearing rain coats and had camera's ready.
 
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