Firstly, Welcome to apug! (I notice this is your first posting).
Originally Posted by richydicky
You'll need 9.1 g of sodium metaborate 8 mol.
The ratio of the molecular weights of 8 mol and 4 mol = 137.88/101.83 = 1.354, which multiplied by 6.7 gives 9.1.
8 mol contains more water than 4 mol, so if you're mixing it into propylene glycol, I suggest letting it sit for 15 minutes at 90C to steam-out the water.
Don't let it get much over 90C or the PG itself will evaporate. Don't ask how I know.