Seachem Laboratories ASM3626 2-Pack Tidal Gray Coast Premium Calcite Marine Substrate, 10kg Tidal gray coast premium calcite marine substrate is ideal for saltwater aquariums Helps to stabilize calcium and alkalinity levels and prevents large pH declines Featured with porous structure and size All-natural aragonite substrates for all types of saltwater aquariums Includes 2 pieces weighing 10-kilogram