I had the aquarium setup for a while to cycle with some Pearl danios, then later added the cardinals (Purchased them in groups of 10) had a few probs with the cardinals but out of 30+ have a nice group of 25ish healthy fish.
Discus were added in two's, as I have not kept them before and didn't want to risk buying anymore to start with incase it all went wrong..
Sofar so good with the discus, no health probs to report! (Touch wood)
Lawrence