Even if a betta has not been kept with a filter, it will do good with one as long as it has plants or a cave or something to get out of the current if it needs to. What do you have in your 10g? Bettas can be kept with many different varieties of fish. I have one in my 55g(see signature). Even older bettas can adapt to new fish. I think that sometimes they get bored when they are alone with no other creatures to look at. My bettas are very curious about the other fish around them. They are not aggressive however, and both of them use EVERY inch of their aquariums. Even the one in the 55g. I had a betta in a 1g no filter aquarium. Now he is in a 10g with 2 snails and he swims around so much more and seems so much happier! Oh, and I feed my bettas a combo of betta pellets and freeze dried blood worms and both of my bettas go crazy for the freeze dried bloodworms and so do my angels.
