When I shake mine, I see mulm come off, and sometimes this will even temporarily visibly cloud the tank.
I think the purpose is severalfold, one just to get it off the stones and make room for new bacterial growth, one to put the stuff in the water column where it can be skimmed along with the nutrients it contains, and the other one to feed corals. Some of it is too big for corals, but some is probably OK, bacteria can be excellent coral food.
Anyhow, like much of the zeovit system the manufacturer says one thing and other people have other ideas, but I'm happy just to follow the instructions, it makes sense to me anyway.
Having said all that there are people who don't shake or pump it and it still seems to work. However I was told by G. Alexander ( a German with an amazing sps tank ), that if he does not pump his reactor daily he notices his corals go paler after a time.
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