Hi, I was at my lfs looking dreamily at live rock and noticed their are two kinds of live rock, one taken directly from the reef, and also a man made version that is left for 9 months in the sea to seed, it costs less has less diversity of life growing on it but still contains a lot of sea life, whats others opinions on this ? it seems good to me, creates jobs, does not damage reefs and is a little cheaper ? would my tank be fine with this rock and maybe a few peices of true live rock to encourage more life, thank you
One thing you are giving up with man-made versus real live rock is the porosity. One of the reasons real liverock works as your bioload is the porosity provides tons of surface area for nitrifying bacteria to colonize which will convert (toxic) ammonia into (safer) nitrates. Large pieces of liverock can also colonize with denitrifying bacteria (break down nitrates) deep inside the rock.
Regarding the other critters that come in on "real" liverock. Personally, I think that 98% of them cause problems down the road....they either die at some point or live and turn out to be a pest.
In my tank, 75% of the rock I used is ceramic made by The Alternative Reef. And the other 25% was established live rock from a former tank, to help "seed" the bacteria population. I am fairly sure my nitrifying bacteria population isn't what it would be if all the rock were liverock. However, I also have sand for substrate which also provides surface area for nitrifying bacteria to colonize. I might be a bit apprehensive to use a high percentage of man made liverock if I were running a bare bottom tank (without considering other methods to deal with biological filtration).
I like your thought process of the man made creating jobs I also like the idea of the rock not being torn from our oceans.
On a personal preference level I like the idea of a 100% pest free rock. Which is what I chose for my tank. Using 25# of dry Pukani from BRS. No unwanted critters, pests nor algaes. I cured it myself using SeaChem Stability for the bacteria. This way I had no die off found with using LR and my cycle time was much faster. It is also much cheaper then LR, a big plus for this reefer on a budget.
Compared to the real stuff none of the man-made products are very porous. The porosity that really counts are the small pores. A rock full of small pores has a ton more surface area than one with large pores. Although pores do need to be large enough for water molecules to pass in order to have any chance of being a biological filter. These small pores are created on a cellular level from coral skeletons that are cemented calcareous algae and are nearly imposible to replicate.
The attached photo is a microscopic view of particular ceramic. As you can see, ceramic can be fairly porous. It would be interesting to get a photo of some of The Alternative Reef ceramic to see how it looks.
@BeakerBob
has a microscope setup for his camera...I'll see about getting him a piece to see how it looks.
It should be noted that I don't necessarily believe that
@gooch
markets his ceramic rock as a biological filtration replacement but rather an attractive way to secure frags and create aquascape that would otherwise be difficult with real live rock.
A lot of man made rock contains concrete as well which tends to be very alkaline. Personally I prefer quality live rock. That creates jobs as well with those who harvest it. pack it, ship it and sell it.
synthetic live rock ?
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I also like the idea of the rock not being torn from our oceans. 
There's nothing like being a Reefer!
