Most quality adjustable heaters require at least 2 gallons, because that is what they were designed for. For that reason, I would say that two gallons is the absolute minimum, because having an adjustable heater really is not optional if you're keeping bettas. However, personally, I will not permanently house bettas in anything smaller than three gallons, but obviously bigger is better. 5 gallons is also a good tank size. The Marineland Eclipse 3 is a nice kit, it's well designed and comes with a fluorescent light and a filter and is very quiet.
Last edited by Adastra; 07-15-2010 at 02:45 PM.