The spec has that huge sponge in the filter compartment. I wouldn't call it "very little". The biomedia it comes with its plenty for shrimp (the huge sponge also holds beneficial bacteria). The only concern is aeration. This can easily be improved by aiming the filter outflow nozzle up and keeping the water level slightly lower to increase surface agitation. An airstone would also work just fine.
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There is very little mechanical, not biological filtration. I'd compare it to a very good sponge filter or a little better under gravel filter in its ability to mechanically filter.
Aeration could use some help, you're definitely right. Here's to wondering if putting an air stone in the back compartment would help.
Actually, I could remove the old pump, use an air pump and connect it thru the old slot. My canister filter would still pull stuff through the old filter. Hmmmm.
How's that for an idea.