i have a ryukin with some brown discoloration on its dorsal fin. the fish is active, eating normally, and uses the fin like normal. i apologize for the image quality, but i include seven images so that you might better get the idea. some other info: it's a 10 gallon tank, using a fluval 2+ internal filter with 2 foam pads and a charcoal pad, 15 watt full spectrum flourescent tube light on for 10 hours a day, little/no direct sunlight, ph approximately 7.0-7.2, water temp about 78-80. i have had the fish for about 2 weeks now, and a few days ago there were 2 lighter brown spots on the same fin that went away in a day, and now this: