Sorry to hear about your losses
For starters, are you using Kent salt? If so, you might have gotten a bad batch of salt where alk measures less than 1 dKH. To find out if this is the case, make up a gallon or two of new salt mix. Aerate and heat to tank temp, add the salt, let it mix overnight, then test alk.
Second, don't let your new saltwater mix longer than 36 hours, with 12 to 24 hours being a better amount of time for it to mix. If left too long mixing, you will find white stuff stuck to the sides and bottom in your mixing container, which means something has precipitated out of the new mix. Also, make sure your water is already aerated and heated to tank temp before adding salt to the water.
Third, don't add anything to the new saltwater. Your new saltwater should not require additives as it should already be close in Ca, Mg, alk, pH as seawater. Adding additives to the salt mix could result in precipitation of some elements. If you have deficiencies in your tank, add the additives to your tank after testing to determine what the deficiencies are. Always keep records of when you test, what you test for, test results and what you add to make up for deficiencies.
I, too, would like to know if the alk in your tank is in dKH or meq/L.