It definitely looks like fungus. Fungus can be treated a couple ways. Salt baths or tea baths. Salt baths are much harsher, but generally work a little quicker. My preferred method personally are tea baths first since they dont strip them of slime coat or damage their gills.
Generally the rule for salt baths are 2-3 tsp of non-iodized salt per liter of water. Youll want 3 tubs. One with the salt solution, one as a rinse tub to get as much salt off as possible, and a third tub to house them in while be treated. 10 minute treatments once or twice per day is usually plenty.
Tea baths are performed using dilute black tea. Black tea has natural tannins that provide antifungal and antibacterial properties. They are also more soothing to their skin. If you wish to try the tea method, brew one bag of plain black tea (check the ingredients to make sure there are no spices or anything mixed in) in 8 oz of hot water for about 5-10 mins. Then dilute the tea in cold water until it is a light amber brown color. They can stay in the tea dilution for hours with no problem. Again, treat daily until the fungus is gone.
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