Oscar fish is ill

Question
Our Oscar has a bunch of red like [appears to be a rash] patches on his upper body and is resting at the bottom of the tank. It seemed to come on suddenly. What treatment should we give him? The tank is always getting clean water with the recommended amount of Fresh Start and filters cleaned regularly.

Thank you for any help you can give us. He has a great personality and we really want to help him.

Answer
Joy,

There are a couple of things it can be. Either ammonia poisoning or red pest disease. Is it possible to get a photo to me of the sick fish? This will make it much easier for me to figure out what's wrong. Check the water and let me know what the ammonia and nitrite readings are. What other fish are in the  tank? If he is not alone, remove him and place him in your hospital tank. I will wait to hear back from you.