Here's a pretty simple herring brine strategy that works for me:

First and foremost: Quality bait. You only want top quality MALE herring in the 1-2yr age class. For some reason, salmon do not like female herring. If you have herring that show any eggs or milt inside them whatsoever, just throw those away...they are way too mushy to troll and are not even worth fishing for sturgeon. To determine which are non-spawning males, it's generally best to count the caudal fin rays and apply the Mylenberg-Lansky Ray-to-Gill Raker ratio. I only use herring that score between 2.3 and 3.3. Also, I have a theory that spring salmon vastly prefer herring harvested North of Whidbey island (more freshwater inputs), or alternatively herring from SE alaska. Or better yet Atlantic herring if you can find them. Fall fish aren't as picky.

For the brine, I find it's best to use water from the natal streams that your target fish is returning to. I'll do a little road trip in February each year, and collect water in 5 gallon bladders from the North Santiam, Mckenzie, Trask, the little White Salmon, the Clearwater, Yakima, Salmon River, etc and use each rivers' water in my brine in accord with the general run timing of each strain. I try to harvest brine water from areas upstream of most road stormwater inets to minimize brake pad heavy metal contamination in the brine. Talk to hatchery staff to determine which stocks are expected to return in what numbers for a given year, and plan your water collection accordlingy. Store the bladders in a cool dark basement to inhibit fungal, algal, and protozoan growth. Or better yet in a refrigerated space if you have access to one.

As for salts, I've done a bit of research and may keep a few things close to my chest. I will say, the most important thing is to make sure that the type of salt you choose doesn't RAISE the pH of your river water by more than 1. A drop in pH is less problematic as it doesn't denature the cytokinins in the herring blood, at least as long as you don't use a metal container. I use HDPE or laboratory grade polyethlene. If you asked me whether magnesium oxide, silicon dioxide, calcium silicate, and sodium aluminosilicate concentrations in various types of salt had any significant effect on salmon palatability, I would shrug my shoulders. Just sayin.

Most commercial bait scents and oils are fine apply to your bait as they are being fished, but I don't reccomend putting them in the brine, because a dead fish's epithelial stomata are all closed, so they don't really absorb anything. Then all you are doing is lessening the shelf life of your mixture, which is a no-no unless you happen to be saavy in the non-sodium based alkaline preservatives that are available now. This is something I plan to learn more about.

You can get a lot more complex with this stuff, but I think for an everyday brine that will catch fish, this is the nuts and bolts of it. I hope this helps someone catch a springer this year!