He means Depth Of Field I believe. and I presume that it was achieved with the camera not photoshop. Much easier to get depth of field like that with a camera then to fake it in photoshop. anyways, what kind of light do you have over that tank?
Wow, it looks awesome. i see a formation that looks like a spiny eel coming out from the rock in the middle of the clearing.
Did you cover those other rocks with something, or is that algal growth? It looks very natural that way.