Here I will explain the basic tank and water conditions for Oscars
TANK SIZE

Well I have seen many arguments over tank sizes in the past but I believe that this is the general rule of thumb.

I oscar at adult size should be in at least a 55g tank and then 25g for every one after that. Now this does not neccessaraly mean you can keep more than two if your tank matches the rule of thumb. You also have to take into consideration temperament of the individual oscar.

WATER CONDITIONS

Oscar like a slightly alkaline water so a ph of of between 6 to 7 would be fine.
Temperature should be around 76 to 78 deg f.
There should be no ammonia readings in the water after cycling so weekly water changes of 15% are a must as well as fortnightly vaccuming of the gravel.

LIGHT

They dont like a strong light so use low level lighting on the tank.

FITERATION

Now Oscars are damm pigs and treat their suroundings like a toilet so good filteration is required. While Im not at this stage going to discuss brands I reccomend a filteration system that turns the water over at least 10 times an hour.
I also reccomend a bio filter like a bio wheel etc

AIR

Getting air in the tank is essential to their survival. This can be done in a few ways. One is to hook up a air pump and stone(I reccomend an air curtin of simular than can be cleaned easy). You can get the desired effect by water aggitation from various filters