It is the fact that white grub is encysted that makes them tough to kill. Salt might very well kill a white grub if it is loose in the water given enough time. But you simply cannot soak a freshwater fish long enough in a strong enough solution of saltwater to kill an encysted parasite. It does work very well for ectoparasites like I mentioned above, and also for ich. It wont do much for the actual ICH on the fish, but Ich has a short life cycle, and during its freeswimming form, it is highly susceptible to salinity. So with the right amount of salt, it cannot complete its life cycle, and dies out
