Any dust, dirt or very small particles will settle to the bottom of tank. Gravity causes that and unless you know how to overcome gravity, it will always happen.
Now then, placing the pipes at the bottom where all the sediment is collecting, and then forcing water through holes in those pipes will stir those sediments up because the water pressure coming out those holes in pipes are stirring it up.
I bet if you left the pump off for a day the water would eventually clear up as all the "material" other than water will have settled to the bottom. This is what I can't wrap my mind around. That's why I asked which direction was the flow.
If I were doing it, I would increase the size of holes in UGF piping and wrap a mesh around the piping if worried about sucking the substrate into it....but I would reverse the flow.
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Similar in principle to doing this...only as described above using your pvc piping instead of having a gravel tray....
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