So... We know sodium kills the monsters, and apparently, sea water doesn't have enough to even inconvenience them... So why does no one even think to try salt while they're searching for sodium suppliers? For that reason, how is it that our "heroes" can lob around handfuls of the stuff, barehanded, without getting their hands burned off?
Metallic sodium is a very different substance from the sodium ions found in salt. There would be no reason to assume that a vulnerability to the pure element would also make them vulnerable to sodium chloride. (Though that's probably more thought than either the producers or the characters put into it).
And speaking of hurting the monsters. We know the cops' sidearms don't faze the creatures. So no one thinks to break out the shotguns? High-powered rifles? The National Guard and automatic weapons? Explosives? Anything other than giving up in despair when .38cal bullets don't work?
I think we are to assume that the local police department is woefully under-staffed, under-equipped, and incompetent. Even after the scientists figure out that sodium can kill them, they don't help the scientists at all secure the substance, and let Hank drive all the way to New York City to get it.