Agreed, give him some things to do, add in sand or gravel, toss in moss balls (he may shred them or just move them around, I've seen them do both), toss in some small pieces of driftwood for him to move, toss in an old sponge filter for him to tear apart or move around, I put my tank near a window so the oscar could look out at the passing cars and squirrels and birds. I fed my oscar everyday, I'd feed him a small handful of pellets one day, the next day I'd feed him something like silversides, shrimps, prawns, nightcrawlers, crickets, etc. Doing more water changes would be beneficial too.