Are they about the same size? I don't see any problems with it but then again I keep a firemouth(about 3") and small(maybe 2.5") convict cichlid with guppies and it seems to work out pretty good. I say give it a shot and keep an eye on them for abouta day or two. If there are any problems then take the problem fish out(the fish that is being agressive, because peaceful fish should not be punished ). If there aren't any problems in the first couple of days then they should be ok together. Good Luck.