You are upgrading by leaps and bownds!
Or Fiji mud. There are a lot of them on the market. I used Fiji on a softy tank and found five things of note. 1. It dose not need to exceed 1" to function as a nitrate reducer. 2. It grows a ton of micro organisms! 3. Don't disturb it unless you have time to let it settle. 4. Macro algae root in it like crazy. 5. Sponge growth was faster in that system then any other I have tried to grow.
So if your thinking of trying it make sure the water flow does not stir it up.
I am just throughing ideas at you that you may not have thought of. I am not pushing mud on you at all.
Zombie snails. Lol. Good call rise from the ground
On the tumbling thing. It all depends on the type of media used. Gfo tends to break down into dust if it tumbles to much or to hard. The idea is that some media gets caked with gunk or gets stuck together and water "channels" around the media leaving much of it unused. Also the thought is if it is floating in the water more area of the media is in contact with the water there by making it more effective. Biopellets tend to stick to one another and grow anaerobic bacteria that can become very harmful to the system, along with this BPs also benefit from tumbling by knocking off the biofilm that naturally grows on them. The bio film is then directed into a skimmer to be removed from the system. The biofilm is what is taking up the nitrates and small amounts of phosphate so by skimming it out you effectively locked it up and removed it from the system (ideally).
To sum this all up let me know what media you want to use and I can steer you in the right direction when flow is in question.