Miracle Grow is no substitute for F/2. It's formulated for terrestrial plants and does not have the vitamins and trace metals that phyto need and what it does have is in the wrong amounts. It will grow phyto but that phyto will by no means live up to it's true potential.
I can't figure why anyone would use Miracle Grow, other than it being available at the corner garden center. For about $25, shipped, one can buy a pack of the ingredients necessary to mix up a concentrate of Guillards media that will feed about 3,000 gallons of phyto cultures. That's less than a penny per gallon of phyto that is high quality and nutritious. Yet hobbyist that will spend lots of money on lights, controllers, pumps, and corals will go and buy Miracle Grow that will grow phyto with the nutritional content of potato chips
