I agree with Jeff, in my pic, those fish with that advanced case of ick, were cured using only salt from the hardware store, either rock or water softener type.
When I treat it is usually a bank of minimally, 200-300 gallons, and between 7 and 12 lbs of salt is needed to bring that volume of water up to a salinity that will kill emerging ick (at least 3.5 ppt (parts per thousand), as it pops from the cysts on the fish.
Just for reference, full strength sea water is approx 35 ppt.
By the way salt (NaCl) is salt, whether its rock, kosher, aquarium salt, it all works, and is also all the same mineral, just a different degree of size in crystals.