I've been meaning to comment back on this.
For me, I was seriously over feeding my plants. I changed out the water, putting in 1/4 of the Miracle grow and Epsom salt that I had been using. Now my tomato plant is growing like crazy! I also have an eggplant and okra plant growing, and there is no yellowing or brown spots on any of my plants.
I an using roughly one tablespoon of Miracle Grow for Tomatoes, one teaspoon of Epsom salt, and one calcium pill crushed into a powder mixed in 5 gallons of water. My ph is around 6-6.5.