I was hoping you'd reply.

It's a 20g. As for the filtration being "strong" -- what classifies it as strong? They don't seem to have any trouble with it and it doesn't create any major current. They aren't hesitant to swim near the filtration system and it doesn't seem to affect their swimmswimming abilities.

Should there be a heater in the tank if I put a betta in it? Our house lowers to 61*F during working hours, since the dogs and cat have coats and we're out.