Many life forms, especially those with hard shells or stony skeletons (like LPS & SPS corals) coraline algae & more are greatly affected by Calcium levels. We want to have a level between 380 - 450 ppm. Red Sea Reef Foundation A is a liquid calcium additive that will easily increase both your Calcium & Strontium levels. Not sure what your Calcium levels are? Be sure to purchase my Red Sea Foundation Pro Test kit & find out!