Thanks everyone! I set a few up in a new 30 gal tank at my g/f's house with one cup of sand and a small real rock from my tank, and within two months, you could see coepods going in and out of the holes in my homemade rock. It's been almost six months since I set her tank up, and there is good coraline algae growth. Below are the steps I used to make my rock:
Materials needed:
Portland Type I/II Cement found at any HD or Loew's (Type III is best, but difficult to find), Oyster Shells (usually can be found at farm feed/supply stores...people have substituted this w/anything from plastic sawdust to macaroni, but I prefer the oyster shells), Aragonite Sand (or any type sand to use as your mold... but aragonite is best), fresh water, a bucket (I use an old ocean salt bucket) or similar type container to mix the concrete in, a deep box (preferably styrofoam because it helps to retain heat, but any should do), a small gardening shovel to mix the concrete, and rubber/latex gloves.
The following steps I use to create about 30-50 lbs of rock at a time:
The Mix:
Pour 28 cups of oyster shells in your bucket.
Add 7 cups of cement.
Add 8 cups of fresh water (it should be about the consistency of cottage cheese... though a bit thicker, so add/subtract the amount of water you use based upon how thick you want it).
Then mix thoroughly (the hard part).
The Mold:
Pour the aragonite sand in the box you're using... the deeper the better (for more interesting shapes).
Dampen the sand with fresh water to the point that it will hold it's shape.
(now the fun part)
Dig out any shapes you like... and add concrete!
Cover what was done with the remaining sand, and let it setup for two days.
Carefully dig your new rocks out of the sand, and rinse w/fresh water (I always like to use a paint brush to brush away any excess sand so as not to waste any sand).
...and the MOST important step:
Curing:
Place your rocks in a trashcan (or any other suitable container) filled with fresh water.
Do a complete water change every week.
Give it a minimum of 5 weeks to cure.
Check your PH regularly till it's down to 8.3-8.5.
Then enjoy your new rocks!