Most aquaria with stony corals needs an additive to maintain alkalinity at a optimal level.
The most common additive for alkalinity is sodium bicarbonate.
It can be used in its solid form or you can dissolve it in water for use with a dosing pump.
Sodium carbonate can also be use, but it is more consentrated and it has a greater influence on pH.
IMPORTANT NOTE:
Some manufactors sells "Carbonate mix". These might be a mix of sodium bicarbonate and sodium carbonate, so can't use the predefined additives in the calculator.
There are two common units for measuring alkalinity, dKH and mEq/l.
The calculator has a predefined parameter for both, please make sure you choose the one matching your testkit.
Recipe for liquid dosage
Hans-Werner balling: 84 g / liter RO water