Just so you know, evaporation and refill doesn't reduce the concentration of any chemicals in the water since only water evaporates. Some concentrations, such as Calcium Hardness (CH), can increase since any CH in the fill water gets added. It's only water replacement, so a partial or full drain, that dilutes or removes what has been added to the water. So your CYA was probably still pretty high though it does drop some over time, usually around 5 ppm per month though at higher CYA levels it may drop faster than that.