"I would love yellow tangs, firefish & seahorses. And the tank should be 54 litres approx. But i dont know which marine fish are preditory and which are community??? HELP ME!!!!! Cheers Joemuz"
Well in a 54l tank ANY tang is out of the question. Firefish would be ok you could have 2 or 3, As seahorses (SH) go You'll have to have a special tank for them b/c they are slow eaters and if you house them with fish the fish will eat all the food. Also SH's arn't very good swimmers and so the flow needs to be quite low.
You might want to look at things like Gobys or the smaller Clownfish.