Black Fin and Tail

[bosdabny]

Hi there,

Not sure what is wrong. I have one male guppy in a 3 gallon tank. Today I noticed that he was real lethargic, didn't want to eat and his tail had a concentrated area of black, as did his fin. I checked the ammonia and nitrate/nitrate, and pH, all were normal. I did a water change and he seemed to perk up a bit, but not completely. The blackness has seemed to disperse throughout the tail. I've tried to find these symptoms somewhere to find out what it could be, but it doesn't fit the profile for a parasite or ick. Any info anyone could give me would be most appreciated.

Thanks!

 

[bosdabny]

I have been changing the water everyday and he perks up, but he still has black throughout his body and is listless. Is there anything else I might do?