Hi dayth
Best to do the coral before the fish, and space out the introductions. Some corals are quite healthy when purchased, and when subjected to stress (upon introduction to a tank) can proceed to nuke the tank in irritation. Allow a settling in period between introductions and observe for stress signs like excessive mucus production, shrivelling, etc.
Good hard corals for beginners include Candycane/Trumpet coral (
Caulastrea sp.), and maybe some of the Pineapples (
Favites or
Favia) --they are among the more forgiving species, ....but you still need to fully undertand the calcium, lighting, and feeding requirements of such
stony corals before attempting to husband them.
The most important shift in thinking, when moving from FO to a true reef, is that while there is now less distinction between the "
biological filter" and the tank itself.
It's not just bacteria at work: everything is eating the poop of something else, so good biodiversity and balance and especially proper biodensity (50 gallons can support only so many upper-hierarchy animals) are the ticket.
hth,
horge
