plenum's provide the same thing as a DSB
and were the "typical fashion" until the benefits of a DSB
were discovered. the water layer provides an anerobic area for removing nitrates, the same thing a DSB
for your sand, buy 95% southdown, then just a few pounds of LS
from your LFS
or a local fellow reefer. IMO
, don't bother with the bagged "live sand" as I fail to see any actual value to it. This includes attempts to contact the manufactures on details with no response from them (there was a thread here where I posted my emails to them. I never got any response)
southdown becomes LS
over time, the majority of which happens during the first cycling of your tank.
is anywhere between 4 to 6 inches in depth. Most will say 4 is a bare minumum, some will say its not enough and that 5-6 is minimum.