The sad thing is you may try time after time and suddenly the problem disappears without you knowing why. A little lino (to harden and fill out) added will likely help. Once you get the melt level down in the pot, a good scraping of the pot surfaces should float what contaminates are left.
The speed you fill the mold and actual mold temp will be close to your past experience. Changing to a bottom pur doesn't alter that..