For the past few weeks I've been trying to cultivate a sourdough starter and I've run into a bit of a rut. I'm using Glezer's firm starter recipe out of Artisan Baking. I've been feeding the starter regularly as per her instructions. I have it in a warm environment between 78 and 82 degrees. My problem is that I can get it to triple within about 12 hours or so, but I can't seem to get it to the point of quadrupling within 8 hours, which seems to be the goal. We've been at it now for 12 days and I can't seem to get it to rise high enough or fast enough. Also, it seems that if I just add the white bread flour it doesn't rise nearly as well as if I add the bread flour mixed with about a tablespoon of dark rye flour (total weight of flour remains at 90 gr.). The bread flour I am using is organic hard red spring wheat - 12% protein. When I feed the beast it looks healthy, nice webbing, lots of bubbles, sticky texture. Any thoughts on how I can get this starter to perk up?