I'm in the middle of reducing my CYA to appropriate levels. I did a partial drain and refill which brought it from around 120 to 100, then I used Bio-Active which brought it down to 60. Neither of these methods are fun... drain and refill is expensive and wastes my DE. And Bio Active is expensive and has to be used with FC under 2, meaning algae is all but guaranteed.
I'd like to have CYA between 40-50. How long will it take, roughly, for this to happen naturally (evaporation and refill, and rain water dilution)? Or should I bite the bullet and do another drain?