You said these were not the new leaves? If they are old leaves near the bottom they could just be dropping from age. As a plant matures it will shed old leaves that are no longer producing food. The fish emulsion wouldn't be any problem. If you used the Miracle Grow according to the instructions that shouldn't be it either unless you sprayed the leaves with it when it was very hot and sunny. That could burn the leaves but it would turn them brown and crispy looking not yellow. Unless you get a soil test first and it says you need it I wouldn't put Chelated Iron on it. Both over and under watering will also produce yellowing leaves so make sure it's getting the right amount of water.