Our Coral Essentials, Coral Power Trace-A is a blend of strontium (50,000 ppm) and barium.  Strontium in natural sea water is in the order of 8-10ppm.  Keeping strontium at this level is advisable and not outside the range of 5-15ppm.  Anecdotal evidence has shown that strontium at below 5ppm in the marine aquarium is detrimental to coral growth.  For the advanced aquarist strontium levels in marine tanks should be checked regularly to determine the take up in your system.  Calculate strontium usage by testing regularly, then simply calculate dosing requirements to suit the depletion rate.  Then continue a check of the strontium levels every week or two.