Can only reply very briefly - apologies. If fluffy = fungus. If not fluffy (or scar but fluffy) = likely battle wound or injury from tank decor. In either case, best to ensure optimum water quality at all times, esp now, to promote healing - 0 ammonia, 0 nitrite, 20 nitrates (or <20 above tap water level). If fluffy, sometimes drops off of its own accord after day or two; otherwise treat with anti-fungal treatment.