The GFO moves throughout you just don't want it to move too violently so too speak, the bottom layer of GFO slowly moves towards the top then back down, the top wouldn't show any movement otherwise. I've been using as is and haven't had any flow problems through the GFO or carbon, I set it and forget it (but do check the tumbling). I don't understand why people insist on a high rate of flow through the carbon, I follow Eheims philosophy of filtration, it's not the how fast you can filter the water it's a matter of the quality of the filtration, more contact time = better filtration.
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