seems to me with a little gap here and there your original plan of stacking might work. i would definitely put 1 layer of micron pad before your impeller though to keep bits from intruding there.
i could be completely off as i don't own a 2217, but that's my thought.
Just turned on the secondary polishing filter for the first time to test a few things. By the way, Kens Fish really came through with replacing the busted 2217, so keep them in mind as a vendor.
So, my purigen is not in yet. And I dont have a good way to keep all the bits of polyester out of the motor, as you suggest. I am going to soak them in water and shake as much loose as I can, but for now I wanted to test exactly how many pads I can stack up without restricting flow. Obviously, the longer I have the thing running, the outflow will slow as the filter clogs. But check this out:
Test 1: 1 x Blue eheim filter pad, 4 x fine white eheim filter pad, 1 x black (carbon?) pad. They are stacked in order as list, from bottom to top. There is obviously alot of empty canister space, which I just filled with water after priming.
Test 1 Conclusion: After running for 10 mins the water is blasting out of the spraybar, as far as I can tell, 4 x white pads restrict flow a negligible amount, at least until it gets clogged. :thm:
What does this prove? Well to me it proves that the Classic 2217 is strong enough to pull water through at least 5 x 1-inch pads. The output is very strong. In fact, it's making me realized how NOT powerful my main filter is putting out water. Time for cleaning after only 2 months?
So, next I want to try even more white pads, or maybe my home brew ones, maybe with a method to space some of my pads apart. Something like 5 pads, then a spacer, than more pads.
Test 1 will run all night, and see what we can pull out of the water. Photos of how dirty/not dirty the white pads got. My tank is full of junk, so it may be a suprise how nasty they get after only 12 hours.

opcorn: