Does salt kill fleas in your carpet?

It does but there are areas of concern it does not address and a better way with carpets would be to use an aerosol like Precor2000 or an adulticide (concentrate) you mix yourself and spray every inch until damp like a pro does although it would take a couple hours to dry out. Getting all that salt out of your carpet and living with it till you get results would probably not be desirable. The aerosol method has its advantages, you can easily treat soft furniture, the droplets are optimum size for deep penetration in your carpet and it contains a growth regulator in the mix- although it is not cheap.