This is an important question for me to ask. For a year I have been running a 24 gallon aquarium with very little water loss due to evaporation. I have recently upgraded to a 125 gallon and feel like i am adding water every time I turn around. My sis who also has a 125 gallon says she looses about a gallon a day depending on the weather. I think that right now I am loosing a tad more than a gallon a day. I keep my home 78 or below and my Average water temp is around 77 as well. I guess this is normal water loss for a tank of this size. I was just curious though as to what others might be loosing with this similar tank size.