Just to clear up some things I've read on this board - mainly pertaining to live rock.
Live rock in this hobby by definition refers to coral rubble, actual pieces of a reef structure, that has been colonized by sea critters, microscopic organisms, bacteria and other marine life. Porosity and surface area of live rock is what makes it so benifical to our tanks. Coralline algae and any hitch hiker creatures are a plus.
Anything else is NOT live rock.
Base rock that has been in an established tank is nothing more than base rock that has been in and established tank. Not too porous, and not near the surface area as "true" live rock.
It's just got bacteria populating it's surfaces, and under the right conditions will become covered with coralline algae.
It still looks nice, can be used in conjunction with live rock, will aid in filtration to some degree - but it's NOT live rock.
Rock formations made from concrete - is NOT live rock. It may serve some function in a reef tank, look pretty cool, but again - it should be called what it is - "agrocrete"
The term "live rock" should be used to describe exactly what it is. Anything else is what "it" is.
Base rock, tufu rock, or any other rock could be considered "LIVE" once bacterial and critters colonize it, but if that is true, then in my tanks I now have
Live Glass, Live Powerheads and Live Acrylic
Stepping down off my soapbox now ......
Brian