I don't know the answer to your last question, but have to say I am surprised to read about Discus being kept with tetras. Although I know very little about discus fish, are they not cichlids? I suppose if it is alright to keep them with tetras then they must be non-aggressive. Also, I know they are very gorgeous fish (the Discus); are they not picky as well, re: heat, ph and such? Just wondering Would love to have some but have not been willing to sacrafice the $$ for them, as they are quite an 'elite' fish and I know they do not come cheaply.