Red Mark On Guppies Tail

[Ginty]

https/www.dropbox.com/s/1tlsbwmz6uj9geb/20140524_203551.jpg

heres a pic of my blue guppy. Ive just done a water test with api kit.
Ammonia is 0
nitrite is 0
and nitrate is 25

any idea what this is?? Ive already added anti-internal bacteria powder because some of my fish had clamped fins and acting lethargic. Ive lost 2 fish in two weeks also for the same symptoms. Hooefully this will clear it but i need opinions please.

 

[WILDER]

Is it more red than pink?
Make sure there no red edging to fins, or red streaks.

 

[Ginty]

It seems to have nearly gone now. I added that anti internal bacteria stuff you said so maybe that helped??

 

[WILDER]

That's good to hear.
Just keep a close eye on him.
 
Good Luck.