I know this is not answering your question but....
There is nothing really magical about media additives. They are an abrasive in a carrier, often a "creamy" detergent base so it "sticks" to the media. Coarser abrasives clean quicker but don't polish quite as nicely.
I sometimes use the Lyman Turbo Brite (for untreated media) 20oz for $14 at LeBaron. (Good for a lot more than one bowl full of media.)
Has anyone tried toothpaste from the dollar store????? Might be a little on the fine side.