Fin Rot

[GetItSahn]

Before buying my last batch of fish I had two mollies, two guppies, 6 corys, snails and shrimp.
 
Then I bought 4 more male guppies and one honey gourami. Since then 3 of the 4 male guppies I bought have died from what I suspect is tail rot. The final male seems fine and the honey gourami has developed black edges and places where the color seem to disappears on it's tail, I just treated the tank with fizz tablets by Tetra.
 
Why are only the fish I have recently bought getting this disease if it's not contagious. Not a SINGLE one of my original fish have showed any signs of fin deterioration or death. Could they just be in bad conditions at the store? Why is this happening?

 

[ncguppy830]

well ill aways start with this what are the water parameters? Its very possible its the stores fault, whuch is why you should QT your fish before you put them in your tank.

 

[GetItSahn]

well ill aways start with this what are the water parameters? Its very possible its the stores fault, whuch is why you should QT your fish before you put them in your tank.

Ammonia and nitrite are 0 which is great i think.
nitrate is 5.0ppm

 

[Feather]

How big is the tank? Is it cycled? And are you using strip tests or liquid tests? Strip tests are notoriously misleading and inaccurate.

 

[Meeresstille]

Looks like the tank is cycled! How long has it been since you've set up your tank?
 
Regarding the infection, your original fish still could get it too, you may just not see it yet, like you did not see it in the new fish on the day you brought them home. I don't know what is in those Tetra Fizz Tabs, and you haven't posted any pictures to see, but from the sound of it I think you might need some Antibiotics to treat your fish! Lots of water changes to keep the water pristine is a good start as well!