24 aqua
The loss of water is evaporation, and the fans would have an adverse effect on the evaporation rate. Some folks have made the slot wider that allows water entry, not deeper, just wider so more water flows through. Something you should not have to do, if it was designed right from the start IMHO. I have heard others complain that if filled to max level, when its shut off it allows water level to come to or slightly above top of tank and trickle out...dunno, never seen one with water in it yet, but that could be a problem for sure. Unless your water loss is from draw and feed throughout the tank, which should be able to be remidied by slot or water inlet size increase, possibly a restrictor placed inside the pump inlet will reduce pump flow. If its due to evaporation, then slowing fan speed will help, but it would entail buying an adjustable wall wart and a bit of rewireing. Either way I would call the manuf and see what they say before I modded anything or made any permanent changes to the thing.