I have had some experience with base rock and can tell you the following.
The base rock you use can only become as "live" as whatever seeds it. If, for instance, you took some "stones" and a piece of live rock from an established tank and put them together, anything that reproduces well in an aquarium and was on the live rock would eventually populate the stones. Anything that doesn't reproduce easily, won't end up on the stones. The good news is, that for the most part anything that doesn't reproduce well won't remain on any live rock for very long. So the demand that things reproduce doesn't affect the base rock much.
You could even get by without seeding the rock at all. If you used 100% base rock and no sand or anything at all, the rock would still function as a biological filter eventually. Bacteria will find thier way into the tank whether you introduce them on purpose or not. On the other hand, it would never acquire any of the sponges, coralline algae, fether dusters, etc that normally are on good quality live rock. Its interesting to note that even in such a sterile setup, you would probably introduce lots of life every time you added a coral. Just the water in the bag, or the plugs or rock will end up seeding your tank. The only problem is that, since you would be counting on reproduction to populate your tank's rock and starting with an incredibly tiny original population, you will be waiting a long time.
So, the idea is to simply start with nearly all base rock and then add a piece of rock from a fellow reefers tank. The only things you need to look at when choosing the rock is how porous it is, and the shape/size. If the base rock is porous and you added a 1/4 lb piece of live rock from somebody else's tank, then your rock will become just as live as anyone else's.
I can tell you that it will be tough to find good base rock nowadays. Hirocks.com went out of business, although their rocks where not porous enough. Reeferrocks seems to be closed. Their website claims they are reopening, but they haven't returned any of my emails or phone calls in the last few weeks. I am currently trying to get rocks from marcorocks.com but they seem too expensive, and I have been waiting for pics for over a week. The owner keeps telling me he will send them in the morning, but he never does. Doesn't sound like somebody to give your money to.
If you find anyone to buy from, let me know your experiences. You should also consider making you own rocks. I have not done it, but other GIRS members have and have been pleased with their results.
Here is a pic of my tank before it crashed. About half of that rock started as base rock. I don't think you can tell which pieces I paid $8lb for and what I paid $1 for.
Brad
