Here's my story:
I have been running carbon for about 4 months. ROX, NOT tumbling, in a reactor. No problem.
Trying to conserve on equipment I added a second reactor for GFO inline with the carbon reactor. I was hoping that I could tumble the gfo, then turn down the flow with a ball valve and NOT tumble the carbon. Well the laws of physics crushed my dreams because without an overflow valve, limiting the flow OUT of the gfo obviously slows down the flow into the gfo, thus no tumbling.
So I thought, so what if the carbon tumbles a little? It's the harder rox, I should be fine.
Wrong.
Within a week of me letting the carbon tumble a bit, my scopes tang showed signs of hlle. No problem for 4 months with no tumbling. 1 week of tumbling and I have signs of hole. The 4 other tangs are fine, but I immediately stopped the tumbling all together.
Henceforth my carbon will not tumble.