I have a 75 Gallon tank with two Oscars in it, but for the last three weeks one of them has refused to eat, her eyes are slightly bulging and cloudly, she's having difficulty breathing and is off colour and her belly seems swollen.

the other oscar is fine and does not torment her in any way, I've checked the P.H. and it's at an acceptable level, I'm not sure what else to do. I have tried to medicate with Triple Sulfa and Pimafix but it has not helped at all.

any advice is welcome! (I appologize but I was unable to get any decent pictures of her, she doesn't like the camera, and I couldn't figure out how to attach the one of her tank mate)

Your fish sounds sick. Can you test your water and post the actual results for ammonia, nitrite and nitrate. How often do you change water, what proportion and how often do you clean the filter? How much do you feed (you should only feed what they will eat in 2 mins) and how often. How big are your fish

However from what you describe it sounds like your fish is suffering from popeye possibly caused from poor water quality.

What you need to do straight way is to do a 50% water change. Add an anti-bacterial. I would add it daily with daily water changes

SConnor wrote:

pristine water and varied foods is the first defense against any fish illnesses.
but since you have started medication without exhausting first all possible
causes, it would be futile to stop now. however, medication with bad water
condition is also useless.

so its up to you, test the water and post the result here so that members can
give proper advise or go ahead with medication without knowing what you are
treating for.