I use Aquapharm Part A & B. Extracted from the site:
Pro Series SeaBalance â„¢
two parts, A & B
Pro Series SeaBalanceâ„¢ is a highly concentrated two-part calcium and alkalinity buffer maintenance system that replenishes calcium and alkalinity with the correct ratio of ions to the composition of Natural Seawater. SeaBalanceâ„¢ also includes magnesium and strontium in the amounts proportionate to typical utilization ratios. Without high concentrations of magnesium, all the calcium would combine with carbonates and precipitate out of the aquariums. Alkalinity is primarily the concentration of calcium, magnesium, carbonate and bicarbonate, which helps maintain a high pH and is essential for coral growth.