We have about a 15-17.5 gallon tank (it translates to a strange size from liters). We also have several bottom feeders, 2 whiptail catfish, 6 kuhli's, 3 shrimp, 2 mini catfish (don't remember their name but they only get to be about 2.5 inches) and a horde of Apple Snails. (We got 3 and then they procreated galore X_x)
The temp stays about 25C (or 77F) During the summer it gets to 26-27C (abt 79-80) I try to keep it cooler by changing water more frequently and we only get about 8 weeks of the really hot weather but even turning off the heater the water stays very warm in summer.
We do have the lights on for a long period so perhaps I should start by trying to cut that down a lot. I usually turn them on between 8 and 10am and turn it off again aroun 10pm.
Thanks for all the advice!