have to put salt for guppy one meh? I thought salt for betta only.

hmmm here's some stuff i learned from the sifu's around here. if your tank is a new one meaning everything is brand new than the cycle would be the culprit.or maybe u placed too many fish into 1 tank? water contains contaminants? what i meant by contaminants are those chemical and biological types which we can't see with our naked eye. also you might have overdosed on the anti chlorine and salt.....duno perhaps if you could describe your tank better like what size, how many fish, any live plants, gravel, how long the tanks has been around i think the sifu's could help you better