My fishes fin

Question
Hi Jaymie,
I'm Jessie. i really don't care about my punctuation so if it sucks I'm sorry. lol i kind of just have a quick question.
I've had my fish for about a month give or take a few. before that i had fish too. but lately i noticed one of my fish cant use its left fin.
You know when fish die they get the white stuff that grows off of them. well it has that on its fin. I'm not sure what that means. oh its a show guppy too.
If its something infectious i didn't know if i should take him out and put him in another tank or what.
So if you can pleaseee help me.. i would really appreciate if u can write me ASAP.

Answer
Jessie,

Sounds like it has fungus. Remove the fish from the main tank and place it in the hospital tank for treatment. There are many different types of medication out there and whichever you choose make sure you follow the directions on the bottle. If the water is clean and changed often it might be whats called a body fungus. If this is the case, make sure you get a  gram-negative antibiotic.