That could be the problem, MG isnt the best for cannabis growth, ive seen people use it with no problems at all but not to often. Most people i know who has used it have experience problems with it due to its time releasing fertilizers which can burn the plans at earl stages in its life.
I dont have any experience with it myself so im not entirely sure, im just saying some of my buddies have.
And that cinnamon on top is probably why it looks like cake mix lol but yeh good thinking, gnats hate cinnamon so hopefully you wont be getting any problems from them