For what it's worth Ase, back to my question - I mixed a simple formula of Calmag and Bloom to roughly hit 1-4-4 and then mixed in the KoolBloom. PPM hit 600 and I was happy with that.
If I find out how to get the measurement exact between liquid and powder I will let you know. I googled for a while and couldn't find the answer but I'm sure it's out there somewhere. I'm guessing you have to measure the weight in g of a set volume in ml to get a conversion ratio. If I was to fill a teaspoon (5 ml) with water, the weight would be 5g, meaning a 1:1 conversion for water. But as the powder is likely lighter, my teaspoon of powder might weigh 2.5g (I didn't measure, just using an arbitrary example) so 1ml would be equivalent to 0.5g.
If that's correct, my 4.4g of KoolBloom would be equivalent to 8.8ml of liquid, and I could calculate the NPK accurately.
I'll need to do some reading on converting between g and ml for kitchen applications. Googling for things like "calculating npk combining liquid and dry nutrients" got me nowhere.