Many English commercial breweries use Burton Water Salts to harden the water, which helps Irish Moss work better to coagulate haze-producing malt proteins, and the harder water also helps provide a crisper hop character. The magnesium provides a vigorous fermentation, and the salt adds an illusion of body to the finished beer. Use according to your recipe or mineral suggestions listed below. If you are doing partial or all grain brewing, add at the start of the mash, or add at the start of the boil for extract brews.
4 grams (~1tsp) per 5 gallons will provide an estimated:
35 ppm Ca
8 ppm Mg
21 ppm Carbonate
84 ppm Sulfate