I'm using gypsum for the first time in an IPA I'm brewing in few days. I made a starter today and thought.... since it's a hopped started, why not add a pinch of gypsum. I used PDME and yeast nutrient along with 2g Columbus hops and a tiny pinch of gypsum. As I usually do with anything I brew, I drew a very small sample to smell it. When I tried the smallest taste I was blown away by the salty taste. Is that from the yeast nutrient? The gypsum? I've done some calculations for the total PPM of calcium and sulfate that i am after in my batch, but if a pinch of gypsum made my 2L starter that salty...... maybe I need to re-think..... Should gypsum additions be calculated using final water volumes (batch size) or total water volumes? I was going to use 33g Gypsum to obtain 191 mg/L Calcium and 460 mg/L Sulfate in 43.4 Liters (total brewing volume). Those figures include additions from the city water supply.
Your brew will definite taste salty with that quantity of minerals added. I would use a third of that amount. 150ppm calcium and 250ppm sulphates is really the upper limit of what you can comfortably use in the beer, and you will still taste a little salt up front, but often it goes with the style.
Here are some guidelines from the HBT wiki,
While there are water sources with higher quantities of these ions used to produce good beer, the brewer will tailor the recipe and use techniques to accommodate the water profile, such as causing some of the solids to precipitate out of solution.
In a homebrew setting, it's best to stick to the guidelines unless you know specifically from experience that adding more ions will improve the recipe. It's best to start gradually - much better to have brew where you think you could have used more minerals, rather than less. Adding too many minerals can result in an undrinkable beer, while adding too little will never ruin a beer, just take it a little off target.
If you don't already have one, a jewelers 0-100g scale, 0.01g precision makes it possible to easily weigh out small quantities of brewing salts. They're only a few dollars on ebay.