have just bought a 90gal tank used and came with a five year old oscar. we got gravel and old tank water with tank. have been testing ph it's at 8.9 to 8.5. Got him 2 days ago and haven't seen him eating yet seems to just hang out at bottom of tank. is that normal? what else can i do to keep him happy & healty? We've never had this big of a tank or a oscar before.

I assume that the tank has been cycled? What are the ammonia nitrite and nitrate levels. He might just be trying to settle in after the move.

oscars are reknown for their ability to sulk if things change in their tanks.
since you just got your o it might take a day or so for him to settle into his new space.
jsut to be safe can you post your water parameter for us ammonia nitrites nitrates and what type of filter you are using. and are there any tankmates in the tank with him.

x2...........

x3 .... welcome 2 the site by the way m8!