White fuzzy areas or tufts can be tough to actually diagnose. Fungus can look like this,
Epistylis looks like this, and Cotton-Wool disease (bacterial Columnaris) looks like this.

Fungus is readily identifiable under the microscope because it looks like strands of human hair.

Epistylis is very easy to identify because the organisms are usually abundant, and feature a long
slender stalk and a body which looks like a wine glass or goblet.

Columnaris bacteria are harder to identify without special stains or a very high powered scope.

I guess it boils down to this: If you scrape off some of the tufty stuff and it looks like hair, it's Fungus.

If it's looking like goblets, it's Epistylis. If you don't see much of anything, assume it's Columnaris bacteria.

Treat with the following:

Epistylis = Salt

Fungus = Peroxide/Potassium

Columnaris = Injections or water treatments