I went to the fish store today and saw they had a silver dollar fish so i decided to get it.. So now in my 40 gallon i have 2 neon tetras and a silver dollar... On the species profile page it says they should be kept in schools... would 2 or 3 be enough?? My wife wants to get a rainbow parrot fish as well and i don't want to overstock the tank... what do you guys think?