IMO the best and most cost effective way to maintain your water level is to is with a peristaltic pump and a bucket for Kalkwasser. Setup a timer on the peristaltic pump so it doeses in the evening after your lights go out and time it so it keep your levels the same from day to day (it will drop some during the day but return to normal at night). A step up is to build/buy a kalkwasser (neilson) reactor that will allow you to increase the amount of Ca you dose. Sumps are good places for heaters, ground probes, evil fish and macro algae for a refugium.
-Erik