GM!! well if you plan to go bigger, and keeping both oscars, id go with 125 gallon as these guys I have are at least 10" long and are getting bigger..I cant go 125 yet, but thats what my boys need...as far as a filter, I have the canister filter for a 125 gallon tank...not sure the brand as my bf got it, but ill find out for you.....all my oscars n jd's get along ...so another would be ok..just make sure its the same size so it wont be a snack
