I don't ever use tap water, always sea or river water... I'm lucky I live near the river...
non-iodized salt, the more the tougher the herring, and a 1/2 tbs. or Mrs. Stewarts liquid bluing... makes them shine.
Remeber, it's like curing eggs, if you cure bad eggs you get bad cured eggs, if you brine bad bait that's what you get. Be picky, select your bait carefully, ever package is not the same. I buy mine by the caes, some years I kull 1/2 of each tray.. Ballard seems to be good, Umpqua bait is the best when the have enough to package, Puget Sound is OK most of the time, Tom Brown is fair, they are from Canada and have good fresh bait earlier than most....... I could go on, but I am getting to excited...
TH
www.thcustomrods.com