my zebra hermits used to be tiny...then they got HUGE. one kept on killing all of my snails...
my friend had a couple that got so big and they terrorized everything they could reach, that he took them to the lfs and fed them to the triggers. don't get me wrong though..they are awesome for wiping out algae. whenever i get algae on a rock, i throw it in my sister's tank (she has the zebras now) and the next day, all of the algae is gone! lol
if your going to add sand and you live in the US, i suggest Southdown Tropical Playsand. i've never used it myself (a friend just got 100lbs of it and is selling me the leftovers), but everybody i know that has a saltwater aquarium uses it. i saw it in action and it looks absolutly incredible.
have you ever used copper treatment with that tank? if so, don't get any inverts and forget about live rock. copper kills.
Tim