I've been trying to grow tomatoes in the Philippines in a small green house for four years. In each separate crop about 20% of my plants become stunted after about a month and the new leaves at the top become yellowish and sick looking. I've tried several different varieties and each one has some very nice plants and a few sick ones. The roots look great. No nematodes. No visible insects. Don't use herbicide. My soil ph is about 4.5, but the water I use has a ph of about 7.2. The ph of the wet soil is about 6. They get equal watering and fertilizer. What in the world is my problem?