How to Treat Pond and Goldfish Fungal Infections

Fish Treatments that "Get To the Point"  > Fungal Infections >  How to Treat Pond and Goldfish Fungal Infections

Koi may or may not even NEED a treatment for fungal infections.

Fungal infections are caused by chilling, mostly. Poor water quality and a sagging pH can contribute. In ponds, fungal infections may come under control just with the warmth of spring. But if you want to treat, there are three medicines that work. Dosing is available on

Formalin Malachite will treat "everything" including fungal infections. It's more "caustic" than it needs to be considering that Methylene Blue will work on fungal infections without the impact of Formalin but sometimes, you want to blast the whole lot, of everything including fungus. 
While saying the above, you should be aware that Formalin Malachite will NOT address issues with crustacean parasites like Lice and Anchor Worms. 

Methylene Blue 
This stain works well for fungal infections and may even diminish certain protozoan infections. It may stain lighter-colored rocks in the system. That staining won't be permanent in my experience. There are two kinds, the powder you have to dose per weight and water, or Methylene Blue in products that are easy to dose for fish systems. 

The above is the methylene blue powder. What you see at right is the methylene blue prep expressly for fish.  The same company makes an 8 ounce bottle. Personally, I'd look at the Kordon product for safeties' sake. 

Potassium Permanganate
The "least safe" treatment of all for freshwater fungal infections, but this 'medicine' has lots of side benefits. Not only will it clear fungus, but it will kill ciliated protozoan parasites, some fluke infestations, it reduces bacteria in the system and oxidizes organic (waste) solids, as well as addressing bacterial infections on the bodies of fish. 
So, if you're willing to take the risk, and you dose VERY carefully, you'll like it. 
This stuff stains 'like crazy'.  

There’s a warm water fungus that kills Koi, and kills them hard. I can tell you how to look at that. For one thing, it happens in warm water, not cold. The treatment for that fungus (once it’s diagnosed is to cool the water with partial water changes and then daily dosing with Eco Lab’s BSDT Formalin and Malachite Green.