The average summer temperature of the aquarium water was about 80 F with a pH of 7.0. No other attempts to alter water chemistry were made. Anacharis grows wild in the waters where I caught the sunfish. The tank is enclosed in a plywood box with removable lid insulated with styrofoam. An air space of about 4 inches surrounds the sides and top of the tank.
Minimal heating is provided using a voltage regulator connected to heat tape.
The heat given off by the heat tape warms the air space. This warm air is pumped into the tank by the air pump and effectively prevents freezing or major drops in temperature. The heat is manually controlled and used only when excessively cold. Below 50 F the food in their stomachs digests so slowing that it can actually spoil before digestion is complete, killing the fish. Besides, I am trying to recreate their natural environment, and minimal feedings in the winter is part of it.