IMO, Oscars or other large fish look better in a 6ft tank such as a 125g, but they can be nicely kept in a 4ft 75g. I'm an oscar keeper and push the envelope by keeping and oscar and a green severum in a 75g. I've had this pair together since they were tiny and have had them in the same 75g setup since 2013. I have a marineland C-360 canister and an AquaClear 110 on this tank, along with a huge pothos plant growing out of the tank, rooted in a marina breeder box. I can keep my nitrate creep no more than 20ppm with one weekly fin-level (~80%) water change.