Just to clarify, your betta will not be "friends" with anything else you put in his tank. If he's aggressive, he'll go after it... and if he's passive he'll just sort of ignore it and stay aloof. It won't actually benefit your betta's wellbeing to have another critter in his tank.
I don't believe that a 3.5 gal is big enough to practically add anything else without overcrowding. I'm not even brave enough to try adding anything else to my 5 gal for fear of overcrowding.
Last edited by Eolith; 01-10-2010 at 04:47 PM.