Since I started kegging I have been pouring about 1/2 pack of bloomed then heated gelatin on top of the chilled keg. It has worked great, clear beer in 1-2 days. But my latest, a Dortmunder Export, is being very stubborn. I used the dregs of one gelatin package, about 2.5g, and saw no change to clarity. A couple days later I added another 3.5g and still no change. This is the first time I've weighed the additions, so I could have been using more than 1/2 pack previously.
The only major difference to this particular batch was the brewing salts used, lots of calcium chloride and gypsum and some chalk to give high hardness (~200 ppm calcium) and moderately low residual alkalinity. The mash pH was 5.3 per colorpHast strips, I have not measured beer pH.
So is there anything I can do to clarify this beer, or is it just chalk that is making my beer cloudy?