Guppy Fin Rot Help

[Gazo]

I've recently purchased some 3/4 black guppys and 2 special German strain pink/whites.
However, after a week 10 of the 14 and the male German have suddenly died after developing what I can only think is fin rot as their tails all suddenly started to waste away - no pics as at work I'm afraid.
The remaining 4 and 1 seem ok, but I obv want to make sure they are ok.
I've ordered some Melafix, which should arrive today - is this the right medication?
Was this something the fish were already carrying, because my tanks are fine and the previous occupants, some homegrown guppys did absolutely fine.
Thanks for any help in advance.

 

[WILDER]

Can you post your water stats in ammonia, nitrite, nitrate, and ph.
Finrot can be a secondary infection.
Melafix is no good on bacterial finrot you need myxazin by waterlife.

 

[Gazo]

Keep forgetting to put my water stats Wilder!

ammonia 0, nitrite 0, nitrate 5, and ph 6.8 - very consistant over all my tanks!!

Got my mother to pick me some Myxazin up from BAS after she had finished her teaching job and leave it behind my wall.
Have treated the little mites to their first dose tonight.
Will let you know how it goes.

Gazo

 

[WILDER]

Ok.
Good luck.