Seachem Reef Fusion 1 (Calcium) raises calcium by 1 ppm per mL per 100 L of tank water (manufacturer data: source). Enter your tank volume, current and target calcium below for an exact dose, split automatically if it exceeds the safe daily limit.
A 75 gallon tank (284 L) raising calcium by 20 ppm needs (20 / 1) x (284 / 100) = 56.8 mL of Seachem Reef Fusion 1 (Calcium).