Awwww sweeeeeet okay, I lost my filters with the brain injury, hard to determine words, but it's super cool I'm helping you.
Think of it like this, promix organic is to grow tomatoes for example. And you get a pretty normal tomato with that soil mix. But now you want bigger tomatoes, so you need more nutes to make that happen. The soil is premixed and has platformed and you can't add or amend to push the potential of the plant from normal to super size. There is a function for every ingredient in soil and plants use them at different times. This particular starter soil is a start to finish, but it isn't what cultivator's would use.
So you are deciding, should I stay with this soil and develop from there, or is there is more efficient medium I can add to that will give me better results. PRESTO, welcome to soilless mediums, the answer to your indoor prayers till you get to the Brix level, which is a whole other world I don't know yet.