i have a 55 gallon with 1 oscar and was wondering if i can get 2-3 1-1.5 inch
silver dollars

As a rule of thumb in a 55gal tank you should keep one Oscar and no tankmates.

However IF your Oscar is a baby (say 2.5" or less) and you are certain to upgrade in a few months (say 4 to 6 mo.) to at least a 80gal tank, then I figure you could add a shoal of 5 juvenile Silver Dollars at 1.5" each, as long as your filtration system is up to handle the bio-load. Silver Dollars are schooling fish and it would be better to keep them in shoals of five or more.

Consider that an Oscar this size usually grows at impressively fast rate of 1" per month. Your Silver Dollars would also grow but at much slower pace.

It would be best to let your Oscar by him/herself if you are going to keep this tank as permanent home. The relationship with you is all this fish needs as long as you take enough time to interact with each other. In home tanks, for some fish (e.g. male Betta), being by themselves is great way of living.

Pepe
Santo Domingo

well i got 3 silver dollars and my oscar went over to them to investigate and he tried chasing one then he gave up and now he doesnt mind

Its not only about if a fish will live with another but the result of having too many fish in a tank to small. your work load will increase as the fish grow, if you dont maintain good water conditions your fish will become sick. 1 oscar in a 55g tank would mean 1 water change a wk. put 3 large Dollars in and you could end up changing water every other day.