Whoops
 

After being out of the hobby for more than a few months, you tend to let's say remember things incorrectly ...

I keep all my dosing additives in either pre-mixed pouches, or use a scale to mix stuff.
So, I bought some 2-part pouches of Mg from J&L and, thinking that I always mix a 1g batch, I mixed enough of their stuff to make 20OZ, but added it to 1g of RO.

No wonder I couldn't get my Mg up !! :doh: