for a single beta, a 2g+ is good. contrary to popular belief, THEY NEED A FILTER AND HEATER. any other fish does, why wouldn't a beta?!?!?!?! it makes so sense and it makes me so bad to see the 20 betas for sale at the store in tiny cups! they are tropical, therefore need a heater, and they poop in the water they live in, it needs to be cleaned therefore a filter. sorry for the mini rant. like i said, probably a 2 gallon or bigger is good. for the filter current, you can eater put a sponge of something or something in front of it. or you could aim the filter output into the wall, up out of the water(but that will make ripples and the dripping noise) or into the back of a decoration.