MG has a product that has TIME RELEASE FERTILIZER in it. if your's has that then don't feed at all. i've heard more horror stories about Time Release Nutes. If your MG is just Peat, perlite and some organic manure for N then yes...you need to start feeding but only lightly. the rule of thumb is: half the rate posted on the box for indoor plants. full rate when using on outdoor plants. full rate outdoors is usually 1tsp/gal. but you're using even less, right? ok so look at the bag if you still have it and look on the front and back of the bag. somewhere you'll see if it has time release or not. man your plants look pretty darn good. the new growth looks nice. i can't see the flaws you see, but overall i'm not even a little worried. i think you'll be ok. oh...did you put some lime in the mix? no? then sprinkle a quarter teaspoon on top and scratch it in lightly. water normally. the lime addition covers Mg also so you won't have to add that either.