Water flow question

I'm in the process of setting up my 55 gal. SW reef tank. I'll be supporting
my LR on a PVC frame.
I'm considering drilling holes in the PVC frame system and connecting an
additional power pump to circulate water from underneath and through the LR
via the PVC support frame system..
Has anyone tried this?
How did you direct the water?
Any advice against this technique?
It sounds good to us. Good water circulation through the LR from underneath
and inside the LR structure will reduce the dead areas from external
(outside the LR) powerhead flow.

We are also considering creating some or all of our substrate from extra LR
by pulverizing and grinding it up then placing it in areas of the tank to
simulate natural reef sand bed accumulation.
Anyone tried this?
What method worked best to convert your rock to sand? (We already have a
sledgehammer :-).

Lastly, How reliable or chemical water treatments for reducing chlorine,
heavy metals, and other impurities from tap water for SW tank use?

Thanx.

Mark and A