Evaporation

I have a 20 gallon tank and a 29 gallon tank with a 5 gallon sump. Both are in the same room and the room is cooled to 74 degrees. Here is where it gets weird; both go through roughly 4-5 gallons of RO/DI water per week. SG level is consistent. I have a 29 gallon downstairs that can go 2+ weeks without using all of the 5 gallons of water (the downstairs is cooled to 78 but this tank has a chiller that maintains 78 degrees).
Any ideas of what could be the disparity between the two rooms?
Thanks!

 

Room temperature, surface water agitation and air flow can influence evaporation.

 

That would mainly be from your air conditioning,you keep your upstairs cooler than your downstairs.When an air conditioner runs,it actually dehumidifies,it collects this humidity on the evap coil,which is the humidity in the air,therefore causing the air to be "more dry" upstairs causing more evaporation in the tanks.There is more humidity down stairs as humid air is heavier than less humid air natually and the fact that your down stairs a/c doesnt run as often pulling humidity from your tank.

 

Thanks for the helps guys, I will try a couple of things mentioned to see if that helps. K+