Yo Ho there Psychitsmike,
Welcome friend, Good question, so let's get down to brass tacks. MG moisture control potting soil comes with ferts already mixed into it. There are problems that come along with it though. I started out with this stuff, and experienced everything that I am talking about.
1. With pre-mixed ferts you are not doing the ferts yourself, but relying on what the company has blended into their mixes, and then bagged up. The bags come with air holes in them, and they often come with a pesky little critter called Fungus Gnats that decided to live in the moist soil. The eggs of which hatch out larvae that will go after the tender young roots. There is a good way to get rid of them, but the little babies can get all burned up by the mix of ferts. If you find that you want to flush your soil, you will compound the problem by releasing even more ferts when you water as the encapsulated stuff is designed to slowely break down with each subsequent watering.
IMHO I believe that you would do much better if you use a neutral potting soil, or blend your own mix. Give the babies a chance to establish themselfs as you don't need to fertilize them right off you know. After your well under way you choose what you want to give them for the vegging, and then for the flowering. Just my $0.02 worth
smoke in peace
KingKahuuna