Evaporation - what is a reasonable amount

[mike31154]

My 77 with open top evaps about a gallon/day, so your numbers are comparable. How's the humidity in your house? If dry, which is typical in many colder regions of our fine land in the winter, that will contribute to a bit more evap from your tank. Also if you have any fans blowing for lighting, that will contribute to additional evaporation. I doubt that adding a filter will change the evap rate that much.