Minimum tank size for an Oscar is 55 for one, 75 for a mated pair. However, you don't have a mated pair. This can cause a HUGE problem, especially if they are both males. Paired males or mismatched males and females will fight each other.
As was suggested earlier, if you want a mated pair, go get 4 Oscars, a huge tank, and be prepared to remove the fish that don't pair off.
Easier solution is to get rid of one fish now, and get a 55 gallon tank, as Oscars really need a big tank.
I have one Oscar in a 55 gallon tank, with a pleco. When purchased, Odysseus was a little over an inch long. Since purchasing him 3 weeks ago, he has more than doubled in size, to almost 3 inches.
If you are going to keep Oscars...I'd recommend overfiltering BIG time. Currently, I have a 60 gallon canister filter and a 100 gallon HOB filter. Between the filters, the pleco, and 2 lazy snails plus a good 20% to 30% water change weekly....I have no trouble with water stats.
