Please excuse me, Michael...and anyone else who read my original post, above.
Sea water, at exactly the right dilution (1%) and temperature (97 degrees), may be absolutely the WRONG thing for a kidney dialysis patient...even if it is only in a bath, or footbath.
Please consult with your doctor about this, if you have any interest in it at all.
The sodium component of seawater may NOT be the level that the doctor prefers for his patient.
I will now go and erase most of my post above, and I sincerely apologize to everyone for writing it.