White fuzzy material on the tail usually means fungus that normally
shows up after a parasitic infection, treat with Quick Cure, which has
formaldehyde for the parasites and malachite green for the fungus. I
would do a large water change (25%-50%) remove any carbon from your
filter, add the qc (one drop per gallon) next day perform water change
(25%) following day qc, next day water change, following day qc and the
last day large water change and add carbon back to filter. Hope this
helps!
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