6gal guppy problem.

[GuppyGoLucky]

Good evening all and a thank you in advance. I'd read other threads but wasn't completely sure.
the tank:
6gallon eclipse (been running for about 3 months now)
4 female guppies
2 cory cats
a piece of driftwood with anubias
3 strands anacharis

i started the tank with water from an outside clean pond and biozyne (sp)
my female guppies have been in the tank for 3 weeks. they were doing fine until a week ago eating, cohabitating.

guppy #1 stays alone either by the heater near the surface, the bottom, or in the flow of water. Also she has white stringy poop. i figured it would be an internal parasite from all the other threads and resources i have read.

guppy #2 is bullying the other two. she "headbutts" and tail swipes #3 and #4 and then proceeds to chase them all over the tank. this started occuring the same time #1 started having the poop issues.

guppy #3 is being fin nipped to the point of the tail fin being shredded and partially missing. instead of the tail looking like a big round circle...it's now got almost 1/4 of it gone, but still swimming fine.

guppy #4 has no problems.
cory cats no problem.

my water chem is 0ppm ammonia, nitrates, nitrites
4 days ago i started feeding the fish antiparasite medicated food, but #1 is not eating it. I've also started them on Lifeguard (all in one treatment) 2 days ago because #1 isn't eating.

any suggestions, tips, and pointers is greatly appreciated! Thanks again!