My daughter has a 10 gallon guppy tank in her room and a few months ago I put her Betta in with them....all was well for a bit then one day one of tha male guppy's back fin was about gone !! So back to the vase with him . The Guppy is fine and his pretty fin is growing back and the Betta is ok in solitaire. I wish he could of stayed in there though.