okay, we better off say that your tank is not big enough for four Oscars. At the moment they are still small but when they reach adulthood, your water will be very difficult to keep in good condition.
Okay, if your nitrite is indeed 10, then your fish should be dead by now. do you actually mean 1.0, or are you confusing nitrite with nitrate? Fish will breathe heavily if there are large amounts of toxins present. I would advise you to get a product called prime. This will neutralize ammonia and nitrite which is obviously good for your fish. Could you please get back to us and clarify the water conditions because I can't see your nitrite being as high as 10, I think you made a typo.