I have understood that salt can kill hens, so you may wish to check on this pretty quickly to make sure.
If you want, you can put electrolytes in the water, though ~ you can order online or pick up at your co-op. McMurray also makes a good vitamin supplement called Avia Charge 2000.
This sounds like a boredom/overcrowing activity. Some breeds/individuals are just more likely to pick, as well. Cannibalism is a nasty habit, and very hard to break once it starts. Nasty way for a chicken to die, too.
Some possible solutions ~
* immediately remove injured chickens and apply Blu-Kote or other antibacterial to wounds until healed. Only return to pen when completely healed.
* use no-pick spray on potential victims. Use pine tar as last resort.
* increase ranging space (may not be viable option)
* provide things to "chew" on -- pumpkins, melon rinds, large squash, cabbages (even hung on string to make it more interesting). There are even seed bars made for this purpose ~ you may want to Google it. Look at the pen ~ is there anything interesting to do in there?
* provide places for chickens to hide/escape/roost. We have perches in the run, as well as wooden "stools" they can run around or sit on/under so it kind of breaks the chasing up.
* watch carefully to see if you can determine the "predators" ~ if it is only one or two, you may wish to cull them. I personally would remove them.
Good luck!