Could be a combination of both: over nutes and watering. Not sure whats in Miracle Grow, but my guess is alot of nitrogen. Did your plant look fine before going to into the flowering stage? If so, that miracle grow has too much nitrogen. Nitrogen is need most during the veg state, then in the flowering stage its needs more potassium and phosphate. I suggest flushing first and stop w/ the nutes. Wait for the top three inches of soil to be dry then start watering again. Then ditch the Miracle Grow and get a fert thats for the flowering stage: anything w/ bloom in it should work well. Start slow, maybe 50% of what the directions state, and work your way up to the recommended level. Also, you only need to water once or twice a week, and only water when the the top of soil is dry and dusty. Hope this helps.