Makes sense, considering I have a sand filter unit on my 35K gallon pool at home. Once you nuke the water with algaecide and chlorine, the sand filter makes that water pretty crystal clear. Of course, we're talking about a pretty closed system. I'd hate to see what two or three quarts of motor oil, some cooking grease, some raw sewage, and various other household chemicals would do to my pool.
We have aeration filter systems on our sewage treatment plants at home, similar concept to the sand filtration. One thing that really hurts their operation is when someone pours a bunch of toxic chemicals down their drain and it kills all the wee beasties in the tanks and basically brings the process to a halt until the sewage can be decontaminated and new microbes installed. Same thing can happen in a septic tank (ugh).
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)