Yup, I've been dosing my NSW 'cause lately my IO has gone for a poop
The Ca and Mg have dropped over the last year

I test each new bucket for the first couple mixes to be sure it's stable/accurate, then I use the Reef Chemistry Calculator for a starting point and do some math from there
I've found lately that I need to boost my Ca a bit, and my Mag a whole bunch;
I've been using up some Brightwell's Magnesion-P powder and add 38.1mls/12g of NSW, and also 1tsp of Dowflake
This is working for me with my dosing pumps using Randy's 2-part and I'm able to keep a decent 7.5/420/1350-1380 weekly with a 10% WC

I don't recommend Dowflake for aquarium use as it has too many impurities. It is only guaranteed to be about 37% calcium chloride and in my experience seldom mixes clear and leaves a greyish brown sludge. I used it for years without issue but it eventually caught up with me.