maybe they are waiting to find out what kind of tank(reef, FO, FOWLR) or maybe not. filtration, skimmer, sump, refugium, water levels. or not. IMO you can use any of the calcium carbonate fine grade sands if you are going to be doing a DSB. i think but i could be wrong. FWIW i plan on using SD TPS mixed with 0 and 1 grade calcium carbonate sand from a diff manufacturer and some live sand ordered online and a couple of detrivore kits from other places.
Tony