Along With The Macro Elements Magnesium And Calcium, Strontium Is An Important Component Of Corals And Other Invertebrates And Needs To Be Supplied Regularly. Recommended Dosage Use The Cap As A Measure. Add Once Weekly One Capful Sera Marin 5 For Every 100 Liters (26.4 Us Gal.) Of Aquarium Water. Sera Marin 5 Was Developed Along With Sera Marin 1 And 2. Strontium And Calcium Are Required In A Certain Ratio.