I agree that side by side comparison is the best way to test if tumbling makes a difference. I am just noting that when I had very little/ restricted flow, there was no difference in my skimmate for 2-3 months. When I increased the flow and the pellets began to tumble, within days, there was a noticeable difference in what my skimmer was taking out. Once again, it might be "anecdotal" evidence, but it's enough evidence for me to believe a little tumbling helps vs. no tumble at all.