urgh.. picked up a few 100 and 150W heaters ued, they all work, anyway what would you use for a 10 divided, It is divided in the middle; so the problem is all my heaters are 10-13 inches long. I will have to sit the heater straight down as they will not fit long ways but even with me sitting them straight down the water only goes a few cm about the min. water line, so if i loose water to evaperation i will bust my heater. a guy at petsmart said use 50w, i figure that would work my heater to death as i use 50ws for my 5.5 tanks and they kick on alot.