about 36 hours ago, I noticed that my fancy guppy has developed a red infection at the edge of his tail fin (see attached photo). There is a larger red area of infection at the top corner, as well as a much smaller red area about 2/3 of the way down on the trailing edge. The photo was taken about 3 hours ago and the larger area has doubled in size since I first noticed the problem.
Otherwise, he is acting normally, is very active and has appetite.
He is the lone fish in a 10 gallon tank. Temp is 78-80, pH 7.8, kH 50, gH 70, Ammonia 0, Nitrite 0, Nitrate 0. Tank has been set up since June, and there have never been any detectable levels of any nitrogenous wastes ( even when cycling, I guessed that this was because there was so little biomass in the tank).
I believe the cause of this was a buildup of organic waste on the tank bottom. The small gravel vac that I had purchased for the small tank didn't work very well( tube was too narrow and it kept sucking up gravel).
The day before I noticed the infection, I had taken large amounts of gravel from the 10 gallon tank and placed it in a larger 20 gallon tank that I was planning on moving the guppy to. When I did this I noticed that it stirred up alot of organic waste from the bottom, which the guppy was exposed to after it got stirred up. Unfortunately I didn't think to take any measures (like a water change) at that time.
After noticing the infection, I changed 25% of the tank water and added a first dose of Triple Sulfa by API. That was last night. This morning I noticed that the affected area had doubled.
I would hate to lose this little guy as I have grown very attached to him, and I am taking care of him for a friend that moved out of the country.
I am worried that the infection is spreading fast. I would appreciate any suggestions for trying to cure it.
When will I be able to tell if the meds are working? If they are not, will I have time to try another treatment before it's too late?