Chunk out the Brass-O. Contains ammonia and not really suited for tumbling media. Either get a dedicated polish such as Frankford Arsenal, RCBS, etc, or use some Nu Finish car polish (Walmart). It won't harm the brass and it does make your media work much faster with a more satisfactory result.
I have not used corn cob media in many years as it has a habit of plugging the flash holes. I use walnut hull media. Dusty as hell when new, but the polish added, and dryer sheets, cut down on the dust. It does occasionally plug a flash hole, but not every other one.....
I usually run my media until it starts to turn dark. It's a "feel like it" thing. FWIW, walnut media lasts much longer than corn cob media, but run what you brung and carry-on. .....