CYA mystery - Salt?

[sbcpool]

Every year I experience that my pool's CYA disappears over the winter. It had been theorized that it was consumed by microbes in the absence of chlorination, but this piqued my interest:

US4003899A - Process for recovery of cyanuric acid from treated chlorinator mother liquor - Google Patents

A process for recovering cyanuric acid values from a reaction mixture wherein salts of chlorinated isocyanuric acid, dichloroisocyanuric acid, and trichloroisocyanuric acid, isomers and mixtures have been formed and which have been treated to convert them to cyanuric acid values in solution, the...

patents.google.com

It seems that high levels of sodium chloride can have an effect on the solubility of cyanuric acid. My pool water hasn't been changed in at least 5 years, and the buildup from topping off and sodium hypochlorite has salt levels near where they would be with an SWG.

 

[jblizzle]

Some light reading for @JoyfulNoise

 

[JamesW]

The salt in your pool has nothing to do with your cyanuric acid disappearing.

 

[sbcpool]

Yeah, on closer reading it looks like it would only come into play once CYA reached levels around 800 ppm.

 

[AUSpool]

That’s a patent, mostly gobbly goop to the average reader. Its not referenced for factual content or peer reviewed. The repetitive use of the term value has me baffled and they don’t say why. What do they want to recover it for? In general its best to stay away from patents.

It suggests that if you add dichlor, trichlor and sodium hydroxide to water and then evaporate most of the water you will get a concentrated solution of cyanuric acid salts.

 

[AUSpool]

The most likely cause of disappearing CYA over winter is from the anaerobic degradation of CYA by bacteria. This Paper explains the degradation pathways. I recall a few journal articles explaining the degradation of CYA in sewage treatment plant anaerobic digesters and there is more here.

 

[sbcpool]

It's an interesting topic (to me). If my case is due to microbial activity it has to be a rapid process. I kept the pool pretty chlorinated most of the winter. There was only a relatively few days where the chlorine might have been low enough to allow microbial growth. The only other thing I could think of is something having to do with the fact that I let the pH get into the high 8's. I'm sure having a fairly strongly basic water chemistry has to have some effect on any acids present.