Many users of this rock do an acid bath and/or a 4 to 6 week soak for the purpose of removing surface phosphates. The idea behind this is to remove any inorganic phosphate deposits on the surface of the rock that may promote surface algae growth.
However, if that's going to be too much trouble because you don't have a suitable place for an acid bath (outdoors only, of course), you could simply set the rock up in the tank, fill it with seawater, buy a Hanna Checker ULR Phosphate Tester (with a 25-pack of reagents), leave the lights off, and simply monitor the phosphate content of the water for a week.
If it's low (<200ppb) and stays that way, you're probably good. If it's initially high or continues to rise, then you can remove the phosphate in the water column with a GFO reactor and/or dripping Lanthanum Chloride (SeaKleer) into the water flow into a felt sock. You'd need to keep the GFO reactor on-line and/or continue to use the LaCl2 treatment until the phosphate level drops and stays low.
