well i read that bigger ones like to be in pairs, but when they are smaller they feel mpre secure in larger groups.
i would have an all discus tank, but i dont want it getting too dirty, thats why i wanted a cat fish or sucker.
if i had three by themselves would they nip at each other?
When I say pair, I mean breeding pair. If you had two, even big ones, they would get very spooked, and very stressed most of the time.
Don't get a Pleco. Most types will suck on to the rich slime coat of the Discus (i've been told it isn't a pretty sight.) I also think that they produce too much waste, in most cases I only recommend Plecos for people with bad algal problems, because they think it cleans the tank, but it really just makes more of a mess (very messy fish if you know what I mean

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3 could get pretty nippy. You would have a dominant one, and depending on his temperment, he could kill the others (thats why you need a back up plan if something does go wrong)