Detritus will always settle at the bottom, but it's so little that it wont cause a problem. I have it too, it's just harmless debri. Now, if you had big chunks, I'd siphon it out although there is pretty good current in the sump space of that filter so it will never settle. Usually stuff that settles there is small pieces of rock too.  I wouldn't worry about it unless it's A LOT of stuff there, then siphon it out.
If it truly begins to be a problem, you can try fitting a small Rio 50 to help push all the crap up into the skimmer. Humm, not a bad idea.
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30g reef tank, CPR CY192 filter w/ DIY plumb running Rio 17HF return, Coralife 3x 9w UV Sterilizer, 3 24W T5-Helios 10K Daylights/3 24W T5-Helios Blue lights, 2 Logysis blue meteor light strobes (moonlights/24 Blue LEDs).
Tiger tail cuke, asst. snails/hermits, asst. feathers, rainbow acan,zoos,shrooms,bubble,galaxea, asst. shrimp, 2 ocellaris,mandarin,zebrasoma xanthurum,pink-spot watchman,red-striped pistol. | 
is it working? 
the skimmer takes out all the little mirco buggers that are bad for a tank...cpr is not my in my field that much...but im sure that you should probably clean the filter material regularly 
