If you ask me, all you need in that tank are Malaysian trumpet snails. I've found them to be excellent at breaking down food scraps and even fish waste in my cichlid tanks. And they will only populate to the level of available food. Great substrate feeders and clean up crew that you don't have to feed or maintain. They mainly come out at night so you'll hardly know they are there, and bigger cichlids totally ignore them. No large plecos adding waste, or other fish for the Oscar's to mess with. I have them in all my tanks now.