ME Strontium concentrate is a pharma grade highly concentrated easy to add additive.  Strontium has been shown to be instrumental in the building of calcium carbonate structure as well as enhancing skeletal strength in coral.  Natural seawater levels are 8 ppm.  The advanced reefer should try to maintain seawater levels.  Depleted levels could affect proper coral development.  Aquarium inhabitants including both soft and SPS coral utilize and consume strontium to grow.    Making it important to replenish that consumption.  Test often.