My question is this can I use the PGA as a direct replacement for PG with ratios for mixing to get the viscosity i need for use in a tank .
As a
direct (1:1, same amount,) replacement?
NO. It would not only thin out the e-liquid
too much, but would also leave the resulting mixture quite harsh. There are also health concerns with inhaling large amounts of ethyl alcohol.
You
could use PGA at a significantly lower level, than the PG... and arrive at a similar viscosity to the original recipe. However, the result may still be unpleasantly harsh, depending on you wife's preferences.
Small amounts of distilled water can also be used as a "thinner"... with less likelihood of adding harshness.
Depending on the device(s) your wife is going to use... and whether the VG has already been diluted with water (sometimes added as an intentional thinner)... and if the menthol concentrate, or nicotine concentrate, has been thinned with ethyl alcohol and/or water (both are better solvents for menthol crystals)... you may not require any additional thinning.
Personally, I would first make a small tester batch just using the VG ingredients you have, and see how she likes it. And, how well it does (or doesn't) wick in the set-up she will be using. Then, adjust as needed.
Honestly, the
need to thin; is dictated by the atomizer being used, and how it is being vaped. Many (most?) of today's attys are designed to accommodate high/max VG e-liquids. But, if she is using an older atty, and/or chain vapes... then there may be a genuine need to thin out a more viscous e-liquid.
