Evaporation - what is a reasonable amount

[spawn]

I lose 5 gal every 4 days on mine, RSM 250 with open top. It's gotten a bit faster since the cold. You should just get an ato...they're the best.

[cwatkins]

I think I lose about 5 gallons every 4 days as well on a 90 open top with hood and 2x 250W MH. My ATO uses a 5 gallon old salt bucket.