In aquarium we may see only some goldfish infected by fungus, As prevention action we must removing the goldfish affected, from the aquarium to stop other fish from contracting the fungus disease. For treatment we can place these fish in an isolation tank and buy a anti-fungal treatment from the pet store and treat them.
There any other method to help infected fish from fungus. The alternative is to place them in an isolated tank, add about 30g of salt to 1 litre of water and leave them in it for around 15 minutes. Please note, do not use table salt for this as it contains iodine which can harm the fish.
While you do not have much control over whether your fish will contract a fungus disease, you can do you part by keeping the tank clean and ensuring there are no sharp objects in the tank that could damage your goldfish's scales.