Hello,
I have 4 discus in a 60 gallon tank with a sand substrate and 3 amazon swords in it. There is also some driftwood. Tankmates are 6 harlequin raspboras, 3 german blue rams, 1 oto, and 11 corydoras. I once had 6 discus, but 1 disappeared after a short vacation, another died about 3 months...