Read this thread of Bens (Littlesilvermax)
Link
. I am also using his chemicals and dosing my RO/DI water with MG and Ca then adding my IO salt. It took a little testing to get the amounts perfect but now every time I mix up a batch of water I can dose the same amount of Mg + Ca to have my water come out at Mg 1300 and Ca 400. Works really well.
I used the reef calculator to get my amounts close then adjusted accordingly after testing
Reef Calculator
Can't beat the price either !!