Originally posted by SWNewb
Depth depends on what you are wanting out of your sand. You can use as little as 1" if it is just for looks, but if you want it as part of your filtration, you need a deep sand bed (DSB) which is 4" or so.
If you want a DSB I would recommend doing it in your sump/fuge area and not in your main tank... There have been several articles on this subject and alot of people aren't aware or informed on the proper maintenance of a sand bed as well...
A DSB isn't required to properly run a reef tank... Fact being that the nitrification and denitrification process that ocurrs in the sand bed ocurrs in the 1" of sand, so basically the other 3" are wasted in my opinion.... Just do some research and there are several articles out there on this very subject