Betta5 he can't use all base rock/ocean rock to start with, unless it's been in a tank and has filtration capacity already.
"To the beginner, live rock, further refferred to as LR, can be quite topic to get familiar with.
LR has some important characteristics that makes the question, "How long have you had this curing?" all important.
Always remember the importance of LR and the effect that it has on your system. A sufficent quantity of quality LR can provide nearly all of your filtration needs. Therefore, inversely, uninformed decisions about LR and the addition of the wrong stuff to your tank can be disastrous.
Now to clear up some terms and definitions.
Live rock Rock that has life on it. This may include some or all of pods, algaes, sponges, bacterias, along with any hitch hiking life that could be stuck in a nook ot cranny. This rock is in an established ecosysytem, be it the ocean, or aqaurium.
Cured live rock This is live rock that has been shipped or moved, and has been cured,(aged), in some type of holding tank to stabilize it and promote the growth of all the good stuff that survived the journey.
Uncured live rock Any live rock that has been ot of water for more that an hour, two maximum, should be considered to have die off on it and be treated as uncured.
Base rock This is the dry bones stuff you find on the shelf at the lfs. It was once live rock, but is now, of course, devoid of all life.
Now here is where it gets a little confusing. The prices of this stuff can be pretty outrageous. I myself have paid over a hundred dollars for a piece of rock the size of a football. And yes, my wife knows, she is the one who thought it was "neat".
Most of the rock we all buy at the lfs is cured rock, or should be. It comes out of the big tank with all the rock in it. This is their curing tank. Very important here to insure that they have had it curing for a couple of weeks at least.
If they just got it in two days ago, you will be buying a rock that will most certainly cause a large ammonia spike in your tank upon introduction. Because it is uncured, and still has die off occuring.
The biggest misunderstanding around; You cannot order LR and have it shipped to you. It is certainly live rock when it is packaged, but during shipping, it becomes uncured.
Curing is easy, however. You get a tank large enough to hold your uncured stuff, put in in, add some lights, a couple of power heads, and a skimmer. You then let it cycle as you would a new tank. When all your parameters stabilize, it is cured, and safe to add to the established system. But unless you are an over the top hobbiest, or have an enormous setup, this can be impractable.
On chosing your LR. Not all are created equal. Some are lighter than others allowing you more volume for the buck. Most certainly try to avoid the stuff that is just a big non porous type of boulder. Try to get the most porous stuff you can. This will give all the life and good bacteria sufficient room to prosper. Also have stackability in the back of your mind. You will want to pile it all on top of one another at some point.
Base rock. Here is a chance to shine. You can easily start out with a third of the volume of your LR as base rock. Try to use this opportunity with the "cheap stuff" to get some interesting pieces as they will eventually become LR as your system matures.
When building a reef, always leave some room for the freebie stuff you will get when purchasing some corals. I have got some real cool stuff at times beacause the coral cannot be separated from it."
This was in that link I gave to you. I wish you'd read it. It will answer a lot of questions you have.
Live rock is porous in nature and has nooks and cranies all over it. The powerheads push the water in and around that rock to give it good circulation/aireation. Bacteria that processes ammonia, nitrite and nitrate will grow inside of it. It does what freshwater canister/hob filters do. Plus, creatures will eat stuff in and around the rock and reproduce (like copeopods). Lots of fish eat the "pods" and having live rock enables us to keep many different fish that we couldn't keep before.
/www.fishforums.net/index.php?showtopic=138236
but am well on my way 
