This is definately not light stuff. I have made it myself and have had good success with it. It will take quite long to become live as it is much more dense than reef rock but it will do the job for base rock for sure. It also takes a bit to cure completely to be reef safe but if this is the same stuff i used it was great after it was cured (in fresh water for a few months).

I had appox 250lbs of my homemade rock in my tank as base rock and it took about 10 months to really take off. The only way you could tell it wasnt real was by the weight. Its a great idea that really works but its quite hard to make a convincing looking rock. They always seemed to have some sort of made made looking feature about them. It could have been the artist being critical though. hehe