I have a nice veiltail in a 10 gallon with a sponge filter and a powerhead rated for a 20. The betta will go lay against the sponge and then swim up and get into the flow from the powerhead. I was a bit concerned when I saw him doing it 2 months ago because I thought I had a weak or dieing betta but now I know it is just one of his games. He is in with a small number of endlers that seem to be able to reproduce even with him there to eat some of the fry.