I had a look at the video link and turned it off when the presenter shook a box of sea salt and called it rock salt. Sea salt is produced by trapping seawater in shallow lagoons then evaporating the water away, the residue is sea salt, this is further refined to remove bits of dead fish and bird droppings then boxed and sold.
Rock salt is everything else and is mined from Cheshire. This salt is the residue which was left after prehistoric oceans evaporated, it is also refined to remove bits of prehistoric dead fish and bird droppings then sold in the supermarkets. If you are going to do a talk at least get your props right.
If you want unrefined rock salt B&Q sells tons of it every year to little old ladies who are worried about the postie slipping on their icy paths. Straight from the mines in Winsford to your bait box.
My koi pond gets treated with salt sold for water softeners and on average has about 20lbs a year added to keep the parasite loading down. It always puzzles me why the salinity drops and has to be topped up every year, I have a large organic filter unit with loads of plants so I'm guessing that might have something to do with it. Perhaps someone on here can explain it to me.
Anyway, back to the bait, adding salt to your hemp at the boiling stage is usually enough to stop the pva melting, you can do the same with any wet particle but I don't know why and I'm sure that at the sort of concentrations we are talking about it will make little or no difference to the fishing.