2many -- I finished my Disabling Conditions course for graduate counseling school about 2 months ago -- and BiPolar was one of the conditions we studied.
I suspect the salt intake directions from the physician have something to do with the Lithium. I looked in my notes and found comments like "ion imbalance, affected by salt levels" -- but I'm not a physician and that's all I could find! Go with what the doc says. Psychiatrists are really good with meds, and lord knows, Lithium has been proven to be one of the best meds for Bipolar. (tell me you aren't just using a family practice doc -- some are good, and some are not.)
If your hubby can't handle Lithium, or if he starts rapid cycling (many mood swings in a day -- like 4 or 5) you might end up with Valproate or a couple of other choices. Just a heads up. That is a possibility.
Ask the psychiatrist for some kind of educational counseling -- you really, really need this for this disorder because the family environment can help stabilize the patient. also, the Family can give the doc a heads up if the patient's sleep patterns change (like if he only needs 2 or 3 hours a night) -- it could indicate a break through depression which can happen on Lithium.
Good Luck. Learn all that you can about this from people who are on the cutting edge....counselors, psychiatrists, the internet. And ask for "best practices" -- "lastest updates in treatment..." "best outcomes" etc. Don't let them give you the old stuff. We've had huge strides in treating bipolar....
((2many))