I have a 55 gallon tank with four 2 inch silver dollars, four 2 inch tiger barbs, and 2 fantail goldfish (i'm probably going to get rid of the goldfish). I am interested in getting angelfish or an oscar. Will these fish work with what I have? Also what else would be a good addition to this tank.
I would get rid of the goldfish. They really don't belong in the same tank with tropical fish. As for an Oscar...They get really big over time. I'm not experienced with Oscars but I don't think that it would be a good fit here. I've had Tiger Barbs and still have a couple of Rosy Barbs...I can tell you from personal experience (once had an Angelfish), that Barbs are fin nippers and will really torment slow moving fish with long fins. Probably not a good idea to put Angelfish in the tank with the Barbs.
They may be small now, but silver dollars get to be over 6". So just the 4 of those would need at least 24gal of your tank. The barbs get to about half that size at 3" max so that's another 12gal of the tank. So that leaves a good 19gal of tank left to play with (getting rid of the goldfish that is). Have you thought about some bottom dwelling fish to break up the soon to be crowded upper part of the tank as your fish grow? Some CorydorasCatfish or Otocinclus Catfish would make nice additions. You could even get 3-4 of each and have a really nice clean up crew for the tank as the Corys eat all the left over food that drops to the bottom and the Oto's will eat any algae you get. Just something to think about to round out the tank.
Brianna, any idea which type of Silver Dollar you have? which is known as the Spotted Silver Dollar is the only one I've found to be smaller, but it's said to be fairly rare at pet stores and still comes in at just over 5". It's not that I doubt you, I'm just curious to know what type you have?
More barbs.. either rosys...cherrys....or danios would work...try a variety of different tiger barbs. Like green ones or albino tiger barbs. You already have aggressive fish in the tank so the angelfish won't fit there...