Compatible Fish

[Furby]

I am about to switch my tank set-up. I have a 3.5 inch Kenyi and a 3 inch Auratus in a 38-gallon tank and it is getting to the point where the Kenyi is bullying the Auratus and the Auratus won't fight back. I know the tank is too small and that is why I am trying to get rid of the two fish I have. I did not find out how aggressive those two cichlids were until after I bought them. I bought them at Wal-Mart and they did not have info on them and they had them in a "mixed cichlid" tank. Anyways, I was planning on getting the new set-up going before adding any fish once I get rid of the fish I have and I was wondering how much the stuff that I put into my tank will lower the pH? I am going to have either sand or pea gravel or both as a substrate and I will have a piece of drift wood in the center of the tank plus a broken 6.5 inch clay pot will form caves across the floor of the tank. I will also have live plants in the tank (Indian Red Sword plant, Java Fern, Elodea, and eventually I might have a Java Moss wall). I also have a bubble disk and a bubble wall that I can put into the tank if it won't hurt the fish to have that much aeration or water movement. The filter that I am running on the tank is an Emporer 400. When I do set up the tank do any of you have suggestions for fish that would go well with Apistogramma Caucatuoides? I am looking for fish from the same region as the Caucatuoides (Columbia) and ones that are just as pretty or more pretty than the Caucatuoides. They would also have to be compatible with the Caucatuoides. Thanks in advance for your help. I posted this in the beginners section but there are very few people in that section so I am reposting here.