Fantail w/ disease

Question
I have a fantail with some sort of problem, but I am unable to figure out exactly what it is.  I have tried taking pictures to local pet stores but they can only give me very vague guesses and I am hoping for something more concrete before I commit to a treatment.

I have a 29 gallon tank with 7 animals in it: the fantail (who is now in a seperate tank until we figure this out), a clown loach, two honey/sunset gourami, a red zebra danio, an apple snail and n african dwarf frog.  The tank is probably about 7-8 months old.  The red zebra danio was the only fish to make it through with the new tank and it's set of problems, the rest of the fish and inhabitants are around 5 months old.  The temp is kept around 72 degrees and I am due to clean the tank tomorrow b/c the snail hasn't been able to clear away the build-up on the tank walls, fake plants, etc.

My fantail in the past literally two days has had a spot on his dorsal fin right where it meets the body on top towards the head.  It started off a whitish blue and it looked like it was red underneath.  It seemed to be smooshing the top of the fin down a little bit and when the tank like shone on it, it was very relective and blue.  In the past two days since I first noticed it, it has now spread to the body and pushed the fin down even more.  It is only a little patch on the body, but the whole thing is symetrical, not splotchy at all.  The whitish blue now seems to rim the red more than cover it.  I moved the fish to a new tank by himself until this is figured out.  Like I said, I have tried searching online and the possible deseases are just endless to me and no one in the pet stores had any definative clue.  Any help would be greatly appreciated.  I am willing to send pictures if needed.
Thanks,
Beth

Answer
It sounds like a fungus. Is it fuzzy? If so, its definately a fungus. You can get treatments that cover a wide variety of diseases/parasites and fungus'. I would recommend getting an all-in-one treatment, making sure it covers fungus and external parasites. No matter what it is for sure, it has to be treated, as it is no natural. How is the fish acting? That is also a good way of figuring out the problem. However, it sounds very much like a fungus. Get the treatment and follow the directions exactly, including the required water changes. Also, it was a very good idea to move the fish to its own tank, this will help minimize the chance of the issue spreading to the other fish. Keep the fantail in the tank by itself until the treatment is finished and the issue is gone. Just make sure to properly care for that quarantine tank just as a normal tank. I hope this helps. Let me know if you need more help.