sick fish! help!!

[galaga-girl]

I have no idea what is wrong with my fish!

Yesterday I lost two and today it looks as though my electric yellow is going to die as well.
I've never seen this before, they can swim around OK but can't move their tails, it's like their whole back half just sort of follows them around. It is really weird.
I've treated the tank for Ich but i'm sure it isn't that. Anyone know what it is and how I can treat it before my whole tank dies??

 

[liv2padl]

how 'bout some information we can use to help you. tank size? how many fish were/are in this tank and what species are they? how big are they? what are your ammonia, nitrite and nitrate readings? how often do you change the water? how much do you change? what's the temperature of the water? what do you feed these fish? what's the pH of the water? etc.

NEVER medicate fish for a disease they don't have.