You use them but do so seperately, adding one fert with water, then the other mixed with water. You don't want to mix calcium and phosphorus together because the cal and P will bind together and become useless. Put them in the soil but do so seperately, or I suppose you can mix in the same water but don't mix them together without water. Don't mix them in water and them set it aside as the longer the calcium and P are together, the greater chance they will mix and become useless.