fish tank bacteria

Question
i have these little white things floating all around in my tank and its already killed all my fish except one and now its all covered in the white things now its a 20 gallon tank and i was just wondering what i should do to get rid of it. also id like to know what this kind of bacteria is so i can stop it from happening in the future.

Answer
do you mean it has covered your fish in white spots?

if so its ick, get some treatment right away otherwise it will whipe out your tank...

to prevebt ick you need to keep the water levels right and minimise stress, also the ick treatment can be added even if the fish dont have it to prevent it.