CaribSea Life Rock Assorted (40LB)LifeRock begins as a sunlit piece of Pleistocene era seafloor thriving with living creatures. Over the next 100 millennia and the retreat of the ocean, this ancient piece of seafloor, now well inland, has formed a pure, aragonite bearing rock. This clean base rock is 97% calcium carbonate with minor and trace elements such as strontium, magnesium, and barium. This base has an amazing 50% void space which will provide residence for billions of water