Hello, Advice for black smudge in goldfish. Aquarium has 1 goldfish and 1 snail with live aquatic plants. I recently treated the aquarium for ich disease. Goldfish recovered from ich, but its fin ends and some scales had abrasions on it. Changed the water and tested water level too (all levels: ammonia was normal). Have done 25% water change every week, with water conditioner and stress zyme. Past few days noticed black smudges on the goldfish. How do I treat this and avoid further problems?