I've been using calcium sulphate for all my brews for a year or two. I read that Burton water has a high permanent hardness due to a very high content of calcium sulphate or gypsum, and that this is one reason why it gained a good reputation for brewing bitter beers, by enhancing the bitter flavours of the hops. Conversely, softer waters found in London were found to be better for brewing milder beers such as porters and stouts. My water in East Anglia has mainly temporary hardness in the form of high bicarbonates but very little calcium sulphate. I particularly like properly bitter beers with a good bite, so I thought I'd add some calcium sulphate. The sulphate adds acidity too which can counteract the high bicarbonate in the mash, improving the yield of malt sugars. I found that the best addition was 12g of calcium sulphate for a 5 imperial gallon brew. I put it all in at the mash stage to take advantage of the acidifying effect. I have no need now to boil or neutralise out the alkaline bicarbonate which is about 300ppm in my water. I also add 5g of Epsom salts (magnesium sulphate.7H2O) as my water is quite low in magnesium. I'm very pleased with the results of my all grain brews since adding the gypsum and epsom salts. The beers have a lovely softness as well as complex bitterness.