As Chris was pointing out earlier, nutrient availability in a soilless media is optimal around pH = 5.8, while in soil media it is near pH = 6.2. An important point here is that if you are using hydroponic methods and start adding macroscopic soil minerals to your media for beneficial bacteria etc., then: you need to raise your pH from the high 5's to the low 6's, back off of the higher Calcium and Magnesium formulas, and introduce urea nitrates in proportion to the soil minerals you added.
