Pierce, I use rare earth magnets to mount my powerheads. The ones I use will each hold 20 lbs. Two of them used opposing one another will hold any coral in your tank. No problem holding 30-35 lbs. Now that's a nice size frag
BTW, when two of the magnets I use snap togther and pinch your skin, you will wind up with a blood clot, immediately. They are dangerous.
swimmer
Don't look like the magnet they used from the picture on the site linked in the first post is anywhere near as big as what you linked.
20 pounds of dead load is a lot less force than 5 pounds on the end of a 6 inch fulcrum.