Concentrated Liquid Calcium provides bio-available calcium for lush growth of purple, pink and green calcareous algaes, snails, hard tube worms and clams. Corals will open more and stay attached to their skeletons better, with regular use. Phosphate & nitrate free! Contains no gluconates, EDTA, or other organics to raise DOC levels, as many competing products do. Concentrated Liquid Calcium alone can provide all the calcium your reef will need, but for maximum results, use Kent Kalkwasser Mix first, then raise calcium level with this product. Strontium addition via use of Kent Marine Strontium & Molybdenum Supplement is absolutely necessary. Use of CoralVite, and Essential Elements are beneficial, as well.