I think the Pentair Aquatics mechanical filter AF-94 will do the job but might clog up quick. It's similar to a RO unit. It uses similar cartridges, I think it uses a 5 micron pleated filter.
I just read the whole thing start to finish. And if you were in WA (or there was some way to ship something like that), I'd pay you to build me a stand here in a few months when I get a large tank. Or I'll have to learn how to do something similar on my own...that slide out for a quarantine is ingenious! Although I'd probably use it for breeding dwarf shrimp... hmm. Amazing job, I'm jealous and definitely bookmarking this thread.