I was just in Miami for a week, beautiful, monumentally humid!

Your CYA won't drop unless you 1)drain and refill 2) have a very big algae bloom (like what happens when we northerners winterize the pool and things go very bad) 3) you have a pool party for a LOT of kids and they splash half the pool water out (this one happens to me). Evaporation won't do it.

That being said, 90 ppm is not bad, and with all the sun you get it may be a better that high.