oscar turning grey

Question
I have a 8 inch Oscar and his color is turning grey.  He is still eating.  I just transfer him to a larger tank.  Is my Oscar dying? I have been checking the water.  Nitrates are high and it show's hard water.  What is going on????

Answer
Hey Collen

this is the Saltwater section, oscars are freshwater, but i can still help you

if the grey looks slimy, its most likely he is increasing mucous production to fight off a parasite, sounds like he might be getting ich. the nitrates could be to blame too, you need to do water changes to get rid of nitrates. I would do a 50% water change, and see if it clears up