Re: Mixing Chilids with other fish, bad idea, good idea?
It depends on which small cichlids and which other fish. Some fish are agressive, some are not (whether they are cichlids or 'other'). Your friend would be wise to research the fish he is interested in and find out whether or not they are compatible with each other.
Definitely have your freind research the actual fish to find the compatability. As you know, at the LFS they "never seem to bother each other" even when you'll see a whole group of cichlids in a small display tank. you'd think it would be a mini war in those water tanks! So the real story goes like this:
Last year in December I bought a small cichlid which I don't even know where it came from in regards to it's origins. I bought him at PetSmart. They always have a tank of "assorted cichlids" with no real identity to species, ...whatever. So I kept him in a 10 gallon tank. On one occasion I put my male betta, and the cichlid in a separate quarintine tank to see how they would fare. I decided that they would be observed for a 10 minute time period. Results; The cichlid was one vicious tough guy. Had I kept them together for longer than 10 minutes the betta would have ended up without any finnage. Just a limp body! I have a picture:
So, at one point when I moved back to my parents house I decided that I was'nt too particular of having dozens of fish tanks. I know I needed my oscar so he went into a 35 gallon rubbermaid tote. he out grew the 10 gallon he started in obviously of course. So I looked at the oscar already hitting the 8 inch mark and I looked at the other small cichlid of only less than 2 inches and said screw it. As you guessed, I threw the small cichlid in with the oscar. Not much hiding places either. That was the point. to feed the oscar. Well it's been 3 month's now and they've decided on being tankmates. It seems rather comical; An oscar and a small cichlid living together. Like Laurel and Hardy.
That's funny about the Oscar and the small cichlid living together. My Oscars were always pretty peaceful, except toward anything that would fit in their mouths.
Anyway, at PetsMart (or other stores) when they say "Asst. Cichlids", they usually mean assorted African Cichlids (which is what is pictured above attacking your betta). African cichlids are VERY aggressive!
I have put young angel fish in with an older male betta, no problems. Yesterday I put three kribs in the big tank, with a male betta, yo-yos, bumblebee gobies, SAEs, and big grouchy CAEs, no problems at all. However, my rosy barbs killed two new otos last week when I put them in (one barb died, one was extremely uncomfortable for a day. They don't attack otos anymore.) and yesterday they attacked a new cory. I guess a good rule would be, potentially aggressive additions should be the smallest fish in the tank, potential new victims should be the largest. And always buy extra otos.
In the past I've had small Pacus and small oscars, in a tank with larger Jack Dempsey's and Firemouths, once the Pacu got big he tried to eat everything else in the tank. Pacus will definitely tear up a planted aquarium. With the 125 I've got now, the Cichlids(all south and central American) seem to leave the plants I have in there alone, but then again the largest fish is only about 4 inches. Although seeing as we got hit by the tornado this week, and power was out for almost 48 days, most of the tank is a giant mess.