Case tumbling/cleaning is probably the most talked about but least important part of reloading. If you ask 10 reloaders what they use in their media you are likely to get 12 different "formula" (don't forget to use the ground monkey thigh bones for your media, absolutely necessary!).
I reloaded for 12 years before I got a wobbler. No ruined dies, no scratched chambers as I just wiped each case as I inspected it (my first step for reloading). I soon went to a rotary and tried a dozen different media with a dozen different media "formula" from pet litter to cat litter (Good Mews worked), wood chunks rice, peas/beans, ad infinitum. Some work some don't. I finally settled on corn cob blast media, 14-20 (tried wet tumbling but didn't care for the mess and extra processing and I don't need pristine case IDs or primer pockets).
No additives are "needed" and I won't use any rouge or abrasive as it can become embedded i the brass. The only additive I use is auto polish/wax for the thin film left on the brass to prevent tarnish. Crushed walnut shells used alone will give clean shiny brass, not quite as shiny as corn cob, but will clean the brass very well. For a tarnish resistance, a bit of auto wax will keep your brass shiny...
Case tumbling is 90% cosmetic. New reloaders seem to be lead to believe shiny brass is essential and they must use a complex formula for media, and a bunch of equipment. I have experience that shows the opposite. I have not ruined any dies or damaged any guns; My "brown" handloads are just as accurate, function just as well as my ultra glossy, inside and out, case handloads. My ego doesn't need a boost from pretty handloads and I don't care what the shooter next to me at the range thinks.
I apologize for this rant (I went passed this thread 4 or five times before my grouchy old man came out), but we experienced reloaders sharing our opinions often mislead the new reloader looking in on a forum for basic information.
Its ok, your just suffering from OFS*. Pretty common past a certain age. You live on this Earth long enough and it is hard to deal with the abject ignorance of young people..
The longer you live, the more you should know. What is hard is remembering from where we came.
*Old F_rt Syndrome