new fishes stressed out

Question
I have a 3 ft tank of tropical water fishes
the tank has been running from a few months
i had 1 dwarf gaurami,few guppies,(male and female) a group of 8 neon tetras,2 black small mollies, about 2 weaks ago my first disease out break took place which started by the black female molly who had some sort of white lips
i checked the water took the water for checking through professional every thing was fine with the water they said to treat it with med
and gave me a bacteria controll medicene made by king british before i treated the water the black female molly died with 2 male guppies
after that i still treated the water to be on the safe side
then every thing started going fine
no other fishes died after that
so after a weak and a half i decided to replace the fishes
and went to a fish store and bought
2 medium size sailfin mollies one small silver molly for my widower male molly
and two male guppies
on saturday evening
then the next morning i noticed a small white patch on silver mollies tail and also saw that the
old black male molly
was really chasing after her stressing her out
she seemed to be hiding all day
and her white patch seemed to be getting bigger and bigger i had some bacteria controll left from before on the pack it said it cures a number of things which included fungus
so i treated the water with it again and before doing this i did do a 25% water change.but today morning i saw the other two male guppies which came with the silver molly were looking very pale too like thier tails colour has changed tottally white and the silver molly just couldnt swim today as if she is waiting to die
now all this is also stressing my beautifull couple of sailfin mollies
please tell me what to do
and also if i am doing some thing wrong
and yeah also give me some info on copper safe  

Answer
Hi Aftab;

It sounds like columnaris. Here is a good article about it with treatment options by our guide Shirley at About.com;

http://freshaquarium.about.com/cs/disease/p/columnaris.htm

I hope they feel better soon......

At Your Service;
Chris Robbins