CYA disappearing?

[Morpheus321]

I can't figure out why my CYA level won't stay up. I live in St. Louis, Missouri, SWG, fiberglass pool, about 4000gal. I opened my pool in late April with no problem. Slammed for three or four days upon opening and passed slam, took CYA up to 60.
All was well for several weeks, then about 2 weeks ago started having problems holding free Cl levels. When I checked CYA, was still at 60, so added CYA to bring up to 70. Still having trouble holding free Cl levels, upped SWG percentage, still not holding free Cl, checked CYA today and CYA=50?!? Nobody has been in the pool because pool temps have been in the high 70's, so no splash out or major water loss.
I have been successfully using TFP method for about 5 years so I am not a newbie and have the correct test supplies and know how to do the tests.
My test results from today: FC=2, Ph=7.4, TA=60, CH=250, CYA=50, salt=3400, temp=77F. Water is slightly cloudy but very slightly (I have become a total pool water snob since using the TFP method so accept nothing less than sparkling clear water ), no green. I have taken Cl up to slam level today and started to slam. Any thoughts on what's going on with the CYA would be appreciated.

 

[PoolGate]

What chlorine level do you normally target?

 

[ajw22]

High pool water temperatures will cause the chlorine to oxidize Cyanuric Acid. This tends to show in water temperatures of 90+ degrees. Every 10F increase in temperature results in roughly doubling the rate of degradation.

Chlorine breakdown in sunlight causes CYA degradation by hydroxyl radicals. This can cause a loss from 2 ppm per month to 10 ppm per month depending on the amount of sunlight the pool is exposed to.

In an area with 90+ pool water temperatures and extreme sunlight exposure 10+ ppm of CYA a month can be lost through degradation.

CYA - Further Reading

www.troublefreepool.com

 

[Morpheus321]

What chlorine level do you normally target?

At CYA=60, target FC=4.

 

[Morpheus321]

High pool water temperatures will cause the chlorine to oxidize Cyanuric Acid. This tends to show in water temperatures of 90+ degrees. Every 10F increase in temperature results in roughly doubling the rate of degradation.

Chlorine breakdown in sunlight causes CYA degradation by hydroxyl radicals. This can cause a loss from 2 ppm per month to 10 ppm per month depending on the amount of sunlight the pool is exposed to.

In an area with 90+ pool water temperatures and extreme sunlight exposure 10+ ppm of CYA a month can be lost through degradation.

CYA - Further Reading

www.troublefreepool.com

Thanks for that info, I actually did not know that. I thought CYA was only lost through water loss. However, my water temps have not been above 80 degrees F since I opened the pool. In 5 years of doing the TFP method, I have never lost CYA at this rate, that's why I am so baffled....

 

[PoolGate]

SLAM time? At least bring your chlorine up to slam and see what it does.