Here's how I made my own Dry Rock.
3 parts Oyster Shell to 2 Part Portland Cement to 1 Part Rock Salt
This rock starts out as Dry and then once added to a system will become live.
Remember that when you are curing your are allowing the rock to leach out any impurities. This will cause PH to rise. Once PH remains stable then the rock is cured and ready to use. This take about 3 months.