ya u definately need a tank heater. I found I good tip u might find usefull for your situation. Get plexiglass the same size of heater and stick it to it. So u can move it around, or from tank to tank, without having to drop 100$ for two heaters. Cold winter up on side, summer on the bottom. It's hard to get temps right. I have like 4 thermometers in there, 1dial,3 sticker type. And 1 un-stuck so I can spot check. They like it 85 and stay in warm corner all day.