I saw this on your other thread
its a 40 but im upgrading to a 90 gallon
To people that know better and care about their fish, a 90g is barely enough tank for 1 full grown Oscar...definitely not big enough for 2.
In all honesty, If I were you, Id take the oscars back until I had a tank adequate for them.
You currently have a 40g which, in an experienced fish keepers hands, could work for the next few months, but if you dont have the filtration required to house 2 Oscars in a 40 and dont do 50% water changes 2x a week, youll be in trouble fast (Hole in the head).
Oscars are terribly messy eaters, put out more waste than smaller growing cichlids and will fight amongst themselves in a small tank, leaving you with daily headaches dealing with them.
Good Luck with what you choose, but Id recommend trading them in for smaller growing cichlids that arent as susceptible to HITH.
Oh, and search for oscar threads here on MFK. There is probably more info on tankmates etc here than anywhere else on the web.