-Yes I have sand in all of my tanks.
The çleanness depends on what you stock.
plant plants in the sand or run your fingers through it occasionally.
you would need a hell of a lot for this i would think.
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You can use play sand, clean fine builders sand, or beach sand. West coast is inert, east coast is more shelly.
Yes. Just make sure your filter inlet is high enough above the sand so as to not suck it up in the current flow.
Use a gravel vac on a 45* angle.
Will regular siphoning near the surface of the sand be sufficient?
It depends on how much your fish mess around in the sand.
Have a good cleaning plan and carry it out regularly. If you use clean sand to start with and clean the bio-waste from teh top then you won't get gas pockets.
Most rooting tropical plants. It depends more on your lighting and nutrients in your water column.
edit suphew: to fix quotes