I wonder if using Brewtan B precipitates out the metals and the CA oxalate a bit, such that the use of lower CA levels is not as problematic for the gushing issue? I shoot for 40-50 ppm of CA, typically. I keg, so I just wouldn't know for sure this as a cause and effect. But I also treat my kegs periodically with a dairy product for removing milk stone and it clears up any beginning issues of beer stone (or late issues, for that matter). I am interested in this topic and may have to run it by Joe Formanek, if I get a chance.