For now I would take the bacterial route.
If the fish are not flicking it not pointing to a parasite at the moment.
A true fungus is quite rare but columnaris is common.
This is the best site on columnaris.
Columnaris has many diguises, can come in a variety of colours, bleached out patches, fluffy, stringy, spots, saddleback columnaris, mouth fungus it quite endless.
How big are the spots on the fish grains of salt size, or bigger.
Columnaris spots are a greyish white colour with a spot in the centre, or a circling of red and the outside of the spot, also they can be fluffy looking.
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