Correct, 2x 5 gal of promix bx, 2.5 gal of Stonington mix,and 1x 5gal of perlite tilled together and put in the octopot bags.
Unless your doing hydro, doesn’t all soilless medium have some nutes in it for the first 2 weeks of growth?
But short answer is yes, Stonington mix is the nutes.
Promix BX has some too which is good enough for the first month of growth.
RO water has nothing in it, it’s just water. You need to add Calcium and some Magnesium to it, roughly 150-250ppm depending.
So if you were feeding with let’s say in the 500 scale, 700ppm of nutes well you add calmag and mix it to roughly 200ppm, then let it sit for a couple mins, and add your 700ppm of nutes which will bring it to 900ppm.
Calmag itself is easy to overdo or underdo, that’s why I always add it first to my water and let it sit for a couple mins. (Before I started using jacks nutrient line)