I have a 10 Gallon tank which had a Plecostomus (I can't spell fish names), a couple of SwordTails, some Neon Tetras, and a Blue Gourami. Well, the Gourami was more aggressive than they said it would be, grew to about three inches, and ate the SwordTails and Neons. Since I couldn't put anything else in with him, the tank held just the Gourami and the Pleco until the Gourami died. Now, however, the Pleco has grown to almost 10" long, and I can keep anything in the tank with him except a few neons because he is so big that additional fish overload the tank!
What can I say. I never had fish before, and I guess it will just be awhile before I learn how to properly select fish for my tank. The pet store people don't seem to know what they are talking about.