Does CYA 'degrade' at any sort of average rate?

[waterbear]

According to Ben -- yes. That is why I said it is a mystery. I always open to a clear pool, no CC, no cya.

In a complete denitrification the reaction will proceed all the way to nitrogen gas which will leave the water. This ususally does not seem to occur in pools but is certainly possible. This anoerbic dinitrification is used in aquariums successfuly with dinitrification filters that control the process so it always proceeds to nitrogen gas. However if they malfunction they produce a LOT of ammoinia which then can kill the livestock in the tank. I suspect in most pools the conditions just aren't right for the process to procede all the way. It is not algae that cause the denitrification. Algae is aerobic (needs oxygen) There are several speicies of anerobic bacteria that are ususally found in soil and in sedemint in ponds, lakes, and oceans that do the denitrification. They need still or VERY SLOWLY moving water (pool pump off), darkness (cover on pool), and no oxygen (consumed by any algae growth, most likely, and once again, no water circulaton) for the process to go to completion and usually a source of sugars or alcohols for food to speed the process up. I suspect the latter is what is missing in most closed pools that exhibit anoerbic denitrification.