you will need to look for peacefull fish over half the size of the bichir. is it p. sengalus? a uniform grey colour? if so then they can grow to around 10"-12". they are not an agreaaive fish as such but if they can get it in there mouth - they will. try looking for medium sisec catfish etc.
If it is P.Senegalus you need a 70 Gallon tank. Not a 29 Gallon. The other fish are fine in there. Just the Birchir. They are really big, bulky fish that are nocturnal predators. Anything that they can swallow, will be swallowed.