Water parameters are fine, this is my girlfriend lol there is no heater, but the tank stays right around 76 as the halogen lights heat the water decently, this is a fluval edge btw, we do 25% water changes 2-3 times a week, could be temperature gradient, all of the fish are eating well and will swim around most of the time, nobody looks off or anything they just seem to enjoy chilling there, or so it would seem