So Ive had a little oscar for a few months now, and he is the most agile friendly fish, he loves when I come into the room and when I feed him he jumps for his food, but two days ago he suddenly started acting mopey. And now he stopped eating completely, his colors are still vibrant and he looks fine, I can see no signs of disease or parasites but he just floats around by the surface and backs off when I come up to the tank. I checked my water several times, ammonia is 0 nitrate and nitrites 0, its been cycled well for a long time, the temperature is 77.5 and I do water changed every two weeks with filtered purified water. I don't understand what could have possibly happened? I did remove algae from the driftwood in the last cleaning but I doubt he would still be upset about this...