I had a 50 watt in my 16 gallon originaly..it seemed like it ran all the time... when I fried it during a water change I replaced it with a 100 watt penn plax... it only runs for very short periods off time and the water stays at 78 where I set it..60 litres is about 15 gallons. A simple submersible heater is all you need. I would get 100 watt model, but you might get away with a 50 watt.