I would NEVER do 3 angels...........that is setup for 1 death.........it is ALWAYS a TRIO OR A SINGLE ANGEL........because otherwise the dominant one will bully the other one............
^ the firemouth will grow rapidly......and the myth thing u heard is true to a certain extent, basically, its true most of the time for appropriate sized tanks...........in a 30G, with an angel......ur 35% stocked to begin with..........
advice
1) for the sand bottom, use a siphon, but suck from like 2-3 inches above the sand to stir up any "crap"
2) remove at least 2 angels......angels need a temp. of 82F.....rams(what kind???), and ANY schooling fish needs to be in a group of 6 or more......otherwise they will stress and die...........especially neon tetras/cardinal tetras
3) remove firemouth(it will grow quickly and can get stunted, will also nip angels fins)
4)get a test kit
u need 1 especially in the beginning
6) even if u had a larger tank and wanted to keep those fish together, the firemouth would start tearing up the angels as soon as it reached 3"+.....
and finally
7) fish get more aggressive as they get older, but in the myth/truth thing what actually happens is that the fish are used to the other fish and know that there is no threat/aggressiveness.......kind of like mutual
how experienced r u? cardinal tetras are quite delicate.........
otherwise.....it seems to be nice
good luck
hope that wasn't too much advice
its just basically stocking.......but i listed each issue in the stocking individually