What do you mean mineralize it first? I study soil and there is no way to flash mineralize the organic amendments in soil. I've seem people on this site talking about boiling and baking soil before going into a tank but all that is doing is sterilizing it so that the amendments take much longer to mineralize once added to the tank. I think someone once read that industrial fertilizer production utilizes heat so they assumed a waterbath or oven would work - in reality you need over 1000 degrees F and extremely high pressures to have any effect. Saying you can do this at home is like saying that you can make a diamond by jumping up and down on coal long enough.
To mineralize soil you are going to need to take advantage of bacteria, there is no other way to do it at home. You could drop all the soil into your compost and water it for several months or you could rig up a bubble barrel and bubble the soil in a water bacteria mixture for several weeks both of which would mineralize some of the soil but not all of it. Luckily miracle grow likes people so see instant results so they load their soil up with high amounts of immediate release (mineralized) organic amendments versus those that need processing - for instance bat guano and earthworm castings are naturally mineralized by the bacteria in the animals gut and are immediately available to the plants whereas feather meal, alfalfa meal, bone meal, and most of the rest of the organic amendments need processing first which makes them a slow release.
Luckily you don't want completely mineralized soil. If it was 100% mineralized then most all of the nutrients would be gone by your third or forth water change; well at least all your nitrogen would be. The non mineralized amendments are what gives the soil it's slow release profile which I assume is why people like to use it. All in all I wouldn't worry about it
Tanks looking great.