Please re-read the directions on the Poekel gewertz. It is not designed to be dissolved in a brine. It says to rub the meat and then place it in a container of water.
This process allows the sodium nitrate to penetrate the meat in proper concentrations to ensure 'preserving'. This also accounts for shorter cure time allowing the sodium nitrate to go into solution along with the other salts and penetrate the cells.
I only mention this because when you are dealing with sodium nitrates you are dealing with a chemical that can produce health problems, immediate and long term, if not dosed out properly.
Personally when I make a corned beef or a pastrami I prefer the dry cure. The additional aging the meat gets during this time, IMHO, provides a more tender end product.