It''s_really hard_ to treat successfully once the fuzz is that visible. BG seem to be really susceptible to certain fungus coming from winter into spring. I think this can be associated with stress, again many factors combine to cause this but water quality has an impact.
The ponds contain many organisms that are present that the immune system can handle in healthy fish.. If immune system is not up to par, things can happen.
If you feed at all, you can mix some liquid antibiotic with some feed-not too much- and if they will eat, healthy fish can overcome some of the issues.
