Erm, I think you should do a lot of research before getting anymore discus. From what I've seen and heard, discus like being in shoals, 5+ and a 40g is not enough room. If not in a shoal, the discus gets stressed and I don't know where you got your info on it being ok with same level fish but I don't think that is true. Never heard of that before. You might want to also look up to see if your BN or other algae eating fish might be attacking the discus. Algae eaters are known to eat the slime off discus, depending on the fish.