Black Moor has White on head

Question
Hello!  I have a moor in with two other fancy goldfish.  He is lively and eating well.  However, he has suddenly got white 'frosting' (not sure how else to describe it!) on his gills and head.  I know its not White spot as I have had fish previously with White spot.  His fins and tail are fine and he is eating.  he is not flicking or hanging at the top of the tank.  the tank has not been moved, changed or had things added to it.  Its a 58 litre tank with a suitable filter and air stone.  He seems happy and is not lethargic.  He does have a scale missing on his side and seems to have cloudy eyes too.  This has been a sudden thing.  Could you give me some advice on what it migh be and how to treat it?  I have tried to research and came up with Velvet disease but do not want to give medication for this in case it is something else.  I have done a water change and added Fish Tonic and Aquarium Salt too.  Thanks for your time

Answer
It sounds like he might have a fungal issue. There are many medications on the market that help with that. Which ever you pick, make sure to follow the directions on the packaging. 58 liters is not big enough for one goldfish let alone 3. The minimum size tank for three goldfish is 150 liters with a filter made for a larger tank.