Copied from the web:
"The problem with lava rock isn't so much that it does nothing (any surface which can be inhabited by aerobic bacteria will be in a marine tank), it's that it is infamous for leaching Phosphates into the water which have a decremental effect on invertebrates and corals, and also cause massive algal blooms. Honestly I'd probably also be wary of the bioballs in such a system because they're likely to capture and harbour such nutrients. If you put any kind of surface in your tank, do all you can to ensure it's either a calcium-based rock or sand, or a neutral virgin plastic so that nothing is being leached into the water."
The bad part about hearing from those that have used it with no problems is not knowing if the rocks have degraded enough over time to start leaching. It may be fine for a couple years, then suddenly kill your entire tank. Also the algae part mentioned would not be fun. I know it's cheap and looks great in a freshwater tank, but saltwater is a different animal am breaks things down much quicker and differently than fresh.