Hey man,
I am using MG Oraganic on my 6 Feminized God Bud plants and also have a small gnat infestation.
Firstly, let the soil dry out as much as possible.
A cheap and easy way to get rid of them is to place slices of a potato on top of your soil. The adult gnats will lay their eggs inside the potato as opposed to the soil.
Leave the slice on the soil for like 4 hours, throw it away and replace it until the gnats are gone.
Adult gnats die in 5 days, it is the larva that poses the problems.
Best of luck,
JJD