You will have critters in your sand provided you find a way to get them started--either by adding liverock or better, some livesand (get some from a local reefer or try and talk the LFS out of a handful). They'll help get rid of extra food and fish poop and generally make the tank more interesting.
If it's been in the tank for more than a few weeks and the tank has cycled, it already contains the bacteria cultures that you want--no need to buy sand activator (IMO, the stuff is questionably affective at best).
Traditionally, livesand is sand that is collected off the ocean bottom, is shipped in a big cooler and contains all sorts of stuff like starfish, bugs, etc. This is different than the stuff available in the last 6 months that has an infinite shelflife. It is merely sand with a bacteria culture already established. It may be a quicker way to cycle a tank, but I think that real live sand is better.
If you have CC, the only thing that you may not get is a DeepSandBed sort of effect. It helps to reduce or eliminate NO3 by converting it to N2 bubbles (you can actually see them). You need about 4-6" of sand to get that. Depending on your tank, CC grain size and depth, you may or may not get the anaerobic region (low o2) required to get the DSB benefits.
A traditionally CC substrate requires an occasional careful vacuuming to keep stuff from building up in it. A DSB is not to be disturbed.
Hope that helps!
Ty
