Hummm. Not trying to contradict someone else but my understanding is that you want it to tumble so that it doesn't settle and get hard because it would make it harder for the water to flow through the reactor. I know when I used it till about a month ago it would tumble and I could regulate how much and I was using a BRS media reactor.
Sorry not sure if I helped or not... I know they have a YouTube video where they use their own reactor... I think it's under mangrove and they don't say they stop it from moving like carbon but do restrict it.