From what you're describing it sounds like levels are critical. Where you live I would believe evaporation could be significant. Only thing I can suggest now is do you remember how things behaved in prior years? Evaporation can vary greatly year to year and season to season. Last year in early spring I chased a ficticious leak for a week only to have it stop. This year, nothing like that. Just strange combination of water temp, air temp, relative humidity and wind. Best I can think of for now.
Al