Whats wrong with my fish?

Ok so yesterday I won a goldfish at Miami, FL house of horrors the water was blue i thought that meant its a boy so it was fine till today, i got two more goldfish(common goldfish) and an aquaview(fishtank includes filter) and some rocks for the fish.Then i added water and the 2 new fish then a little of the blue water and the goldfish and now one common goldfish is dead from fin rot and i just got it and the other is fine but......my other goldfish has fin rot also im very scared for the other 2 that are alive please help me giveme some care tips or tell me whats going on i forgot to tell you ONE OF MY FISH LOOKS LIKE HE IS GANNA DIE HURRY!!!!!!