If you're interested in growing discus as large as their genetics will allow, they are tricks for doing this. It takes dedication, but it's been proven many times by people with show winning fish. You put a group of young fish in a bare bottom tank, crank up the heat to around 86F, feed them a beefheart mix 5 to 6 times a day, and do daily 75 to 100 percent water changes. The water changes are necessary because you are feeding so much high protein food, that the water would be completely fouled after the second day. Most 8" fish are grown this way. Otherwise, such growth would take a long time, if at all.