Very important that you are using kosher salt and not good old table salt. Fish brined with table salt is darn near inedible.
I've been meaning to ask about that... the only difference between kosher and regular salt is the chunk size and the iodine, as far as I can tell. What about it actually makes a difference for the brining process? Does the iodine make that big of a difference?
From everything I've read, the iodine does not make a difference in the brine. Some people have said there is a difference in taste, but from studies that have been done, any taste difference is insignificant, and is more based on perception than reality. The main difference when it comes to salt is crystal size. Most brine recipes are based on Kosher salt, but you can use table salt if you want. It doesn't matter for a wet brine, but for dry brining, you should follow the recipe if it calls for Kosher salt. Kosher salt crystals will melt more slowly than table salt. The common equivalents for salt measurement are:
1 part fine sea or table salt = roughly 1 1/4 parts Morton’s kosher salt = roughly 1 3/4 parts Diamond Crystal kosher salt