Hi GM,
Salt water marks will be NaCl , which is sodium chloride , common salt, which will cause bleaching particularly if mixed with other chemials.
I would start by extracting with plain water which may remove loads of salt , also worth trying an acid rinse.
Bear in mind salt is water soluble so will be relatively easy to remove but will be prone to releasing chlorine whcih will act as a bleach.
Cheers
Doug