HI ! new here.

The powerhead will pull a bit of sand out, not a big deal. You can play around with different locations for it, but still expect it to move the sand a bit.

For the black 'dust'--most likely it's just darker particles that are lighter than the rest. Unlikely to be a problem--though you can use a bit of airline tubing to siphon them out if you like.

Otherwise--looks to be proceeding on schedule!
 
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