sick fish/guppies

Question
I had purchased 2 fish from a little fish stored that said they wont sell sick fish. i don't remember what they were call something with neon in it, not neon tetra though. one was orange the other pink. i had  3 tanks of guppies that i have been breeding for over a year. i put the new fish in the tank with some of the bigger babies and after about 2 weeks i noticed the new pink fish looked deformed. it looked as if it was was in a Z shape. i removed the fish and put in in a tank all to itself. it died shortly after. now some of my guppies seem to have this. about every month i have a new guppy that looks like its spine is bent and it swims funny but they will still eat and they live about a month or so like this. i cant seem to find out what disease this is or what i need to do about it. if you have any answers i would appreciate it.

Answer
Hmmm... there is a fairly common disorder that affects guppies who have been over bred, have poor genetics or who weren't fed sufficiantly when they were young. It also affects older guppies. It makes them look like their tails are broken. Kind of like an "L" shape, but I'm not sure about a "Z" shape? Do you know it isn't one specific fish giving birth to monthly deformed baby? It could be that she's just had enough breeding? Do the pink and orange fish have white stripes down the length of their bodies? They sound  like they're maybe a newer/hybrid Danio?