It is my understanding that I need to purchase a heater for the biocube 29 that I have on the way. I was looking at Jager Thermostat Heater and wasn't sure if I should be getting the 75 watt or the 100 watt. I had heard at one time that this aquarium doesn't actually hold 29 gallons of water so would the 75 watt do the work? Thanks.