Hello; Treatment can depend on what the tank sizes are. I usually try to treat in a smaller hospital tank for suspected fungus. So much less treatment chemicals needed and no chemical stress on healthy fish or the cycle bacteria.
Might also use a dip treatment. I have used methyelene blue as a dip and as a soak in a hospital tank. I have also just put drops directly on a fungus while holding a fish in a net.
Hello; I understand about breeding damage. You do not say but from the photo looks to be a cichlid. They can play rough when spawning.
Here are some suggestions. One is to get the water conditions in the main tanks as good as is possible. If you are willing to post water test results some of us may have other suggestions. Tank sizes and other parameters can be helpful. Just too many potential unknowns to make intelligent suggestions. You are giving useful information in small doses over time. bear in mind you are the only one on the scene and wee are in the dark about so many things. I am guessing based on scant information.
If you have a QT or other small tank that can be used as a hospital tank that would be my best guess suggestion so far. Figure what chemical treatment you wish to use and treat in the hospital tank. Treat the affected fish for a few days with mild doses of medication.
That tank can also be set up as a dip tank. Which has a stronger solution of medication and the fish may only be in it for a few minutes. Say held in the water while still in a net.
The earlier suggestion to do some extra WC and add some salt may be the safest plan in some ways. In clean water with some salt the fish may be able to fight off the infection on the wounds on it's own. This avoids the stress of being captured and moved.
Good luck
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