I don't know if this helps, but I kept Nanacara anomala and Corydorus elegans in a 110 gal stock tank outside during the summer, bringing them in only recently. The temps for the tank were in the mid 90's for highs and down to upper 50's for lows. Once the temps started getting down I put a 300 watt heater in the tank. The fish showed no signs of ill effects and in fact the anomalas bred. Also, their colors were, and are now that they are inside in a "proper" tank, the best I have ever seen. Take from this what you want.