Will Cyanuric Acid Lower over Time?

Cyanuric acid does not evaporate or degrade like chlorine and other chemicals do. It will stay in the pool water. ... The only way to lower the levels is to drain some water and add water with no CYA in it.

Does CYA reduce over time?

Yes, entirely possible. As you point out, there is a testing variance to consider and CYA will naturally degrade a few ppm per month, maybe a little more.

Does cyanuric acid degrade over time?

Due to the fact that cyanuric acid does not evaporate or degrade, the levels continually build up and overtime pool owners are forced to drain their pool.