We originally had our betta in our 3 gallon, with a snail. The betta never really moved much, always stayed in the corner. Once in a while he would float around a bit but that was it, always ended up in the corner again sitting in a particular plant. He didn't look unhealthy, just lazy. The water parameters always checked out ok in the other tank, it was fully cycled. I thought he needed a heater so I added one but that didn't change a thing.
Against what I felt was the 100% correct thing, I moved him to a one gallon tank, along with his favorite plant that I trimmed down to fit. He seems so much happier now, slowly swimming all over the place, going up and down, side by side and displaying nicely.
Could he really be happier in a one gallon without a heater????
Also, can a betta do without the air pump running at night?