OK I'm very much a newbie from a freshwater background....in a FW tank
deep substrate is OK if the gravel isn't too large and the tank has
plenty of plants where the roots pretty much deal with the nasties and
you vac up the rest....from my reading and advice I've been given too
deep in a reef tank has a few problems without the right clean up
crew.....you cannot gravel vac your substrate (a fav with us fw guys) -
if you do that you are taking out the good critters along with the
nasties....From my understanding (and limited experience) dead sand
rapidly becomes live sand if you have live rock....so why spend the
money....

Very much what I have read...and observation on the amount of activity
in my "dead sand" that is now brimming with life after 13 weeks...

Gill