Why is my clean brass not clean?

So before that knockers have their say, ultra clean shiny cases don't help you shoot better but handling fired cases can be hazardous as lead and other contaminants are easily transferred to the skin when reloading. Also, I'm not going to go into talking in detail about the pro's and con's of wet vs. dry (vibratory) cleaning except to say I have been wet tumbling for at least 3 years now and am very happy with how it works over dry, particularly how it cleans the inside of cases.  Not to mention the health benefits that go along with avoiding airborne lead that can be present when dry tumbling. 

Moving along, my recipe for cleaning used Lyman Turbo Sonic and Lemishine with 4KG of cases and 2L of water tumbled for 90 minutes which gave me pretty good results.   But in recent times I had started to notice that the brass wasn't coming out quite so well as it used to with cases not so shiny and kind of pale looking. I thought I'd try something else and bought some MP103 burnishing compound from Aussie Sapphire substituting it for the Lemishine/Turbo Sonic.  Although the results improved they were still not 100%

With not much else to do over breakfast, I researched (Googled) why this might be happening and, of course, with the internet full of opinions about recipes and what to use and not to use blah, blah I saw someone say that cleaning the media occasionally is a good idea.  Really? - aren't the pins cleaned in the process?  Anyway, no harm giving it a go so I threw in a couple of liters of water and a dishwashing tablet and in a few minutes that water had gone black!
See photo below.

I then proceeded to rinse and ran it through a wash cycle again this time I threw in some car wash (it was at hand) and ran it through again.  The water was now looking much clearer and with a final good rinse, I ran 4KG of dirty cases through using MP103 burnishing compound.  I set the tumbler for my usual 90 minutes.  10 minutes later I checked on progress and to my surprise, the cases looked clean already.  Grabbing one out of the soupy mix (using a spoon) its appearance was stunning!  I can't believe the difference. 

A good rinse and separation of media and you can see how they turned out - pretty well like new.