From my experiance (never had discus), cichlids over all will/can pick on large bottom dwellers. I'm sure its a natural thing to do in the wild as large bottom dwellers will eat you, your offspring, your neighbors, whatever they want, when they want. So the picking on in a vast area would just make the bottom dweller leave and there for little damage. In our systems they are locked together. I have seen this with bichirs, and large catfish that dont or cant hide. Angels do it, Africans do it, most of the sa/ca that ive had ive seen to it. Most of the time once the fish moves they stop.
