How to Treat Fungal Infections in Freshwater Aquarium Fish
Grab some methylene blue for fungal infections and follow label instructions. This may stain silicone sealant in fish tanks. But not very hard.
It’s critical to improve water quality and crowding.
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.
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.
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'.