I also have a 100 gallon stock tank outside. It has some water lily's, water lettuce, duckweed, dwarf water lettuce, crypts, watersprite, anachris, plus more that I can't think of right now. In this past week's hot spell, 100 degrees, the tank got up to 90-91 and the fish really didn't seem to mind. In fact the cichlids were more active than they had been, just not at mid-day. Occupants are Nanacara anomala and Corydorus elegans.