The same chemical formula as the 7 part program you love from Red Sea, now in 4 easy parts! If your reef system is without refugium, the Major, Minor, Alkalinity, and Trace Elements, are all used up at a similar rate. Since Calcium is the key indicator of coral growth, the 4-part program revolves around a single weekly measurement of Calcium, which determines the dosages of all 4 parts, and is fomulated for all 4 parts to be used up at the same time. If you use Red Sea's ReefDose, simply set Calcium dose, and ReefDose will take care of the rest. Please note: Systems with refugium should use Red Seaâs 7-part RCP to properly maintain all elements. Dose for 160L/42.2gal.