The buildup of cyanuric acid occurs over time because it does NOT evaporate
nor does it preciptate out, therefore the filter system does not catch it.
Occasional loss of water due to back wash, pump out and evaporation remove
relatively small amounts of water so this build up is not affected much by
these actions. Some users do not have this problem because they either use
relatively small amounts of a sanitizing chemical or what they use does not
contain a "stabilizer" (another name for cyanuric acid).

Obviously each pool situation is different. My comments were meant to
inform, not be absolute.

"Ether Jones" wrote in message
oups.com...

Charlie Morgan wrote:

Pool water gets exchanged through evaporation/ top up,

Does cyanuric acid evaporate?


and backwashing the filter/top up.

That makes sense.