It sounds like your fish has slime parasite disease
Slime Parasites give your fish a coating of grey/white mucus over the body, the eyes can appear cloudy. It may shimmy, scratch, jump and flick against objects in the aquarium - like it’s trying to have a really good itch.
This disease stresses your fish and may make it prone to secondary infections such as fungus and fin rot.
Watch Out! – Treatments can sometimes reduce oxygen levels in the water. If you see fish gasping at the surface, you can increase oxygen by adding an air pump.