Hey man it looks to me like a ph imbalance. Ive never used miracle grow anything and everything ive heard about MG has been bad. Do you PH the water when u add nutes with every other watering? Even 1/4 strength could drop the ph a good 2-3. I would suggest stopping all nutes and just use plain water for the next week then resume the normal feeding schedule. If it worsens during this week then flush the plants with room temp water. Buy some cheap ph test strips from a pool store and test when u add the nutes. Get it between 6.1-7 for soil. Nutes will always lower the ph so add baking soda to up the ph to the desired range.