I broke this down from Ben, {chemmaster and who,s products I use for it}.
23g mix, 150ml magnesium...mix in ro water for awile then add 3 tsp. calcium. Usually mix it overnight or something, before adding salt.
I use for a 5g salt bucket of water.... 37ml magnesium & 3/4tsp. calcium.
I have heard the levels in new IO has been increased but this is still what I,m using. I add no magnesium to my tank itself and usually stays at the 1350ppm range.
For alk and calcium in the tank itself, I use Seachem 2 part. I would add no buffer to IO salt, as its usually pretty high in alkalinity already. Just use whatever is needed in the tank itself. Like mine or the cheaper stuff or any of the 2-parts. Or even when I dripped kalk, the alk. stayed pretty steady with the kalk drip buffering it enough, except for the odd time of adding a small bit of buffer.
. I see Ben posted while I was typing mine.