To accompany Bubbatails excellent ph chart thread here is a chart that displays the avalability of different nutrients at different ph levels.
Adjusting the PH of your Nutrient/Watering solution is of great importance when growing fine bud. When the pH is not at the proper level marijuana will lose it's ability to absorb some of the essential elements required for healthy growth. For all plants there is a particular pH level that will produce optimum results. Marijuana likes it's hydroponic solution to be 5.5 to 6.2 and soil to be 6.3 to 6.8. Although most plants can still survive in an environment with a pH of 5.0 to 7.0.
If the pH is too high, marijuana suffers from a lack of iron, zinc, manganese, copper and boron. If the pH is too low, it lacks phosphoric acid, calcium, and magnesium. At lower pH (more acidic) ranges, diseases can thrive. Normally, plants tend to take up more acidic elements, causing pH levels to increase or drift up the scale.

The chart illustrates the importance of keeping a correct PH throughout the grow cycle.
As I have stated in other threads my favored way of maintaining ph in a recirculating hydro system is to set it low at ph 5.5 and then let it rise upto 6.2 over the space of a few days/cycles, before re-adjusting it back to 5.5 again. In most cases the ph in a healthy system will always rise. I belive this is the best way of managing ph because it allows the plant to experience the full range of ph values that it feeds well in.
So often people that grow in soil make the mistake of thinking or beliving that they don't have to adjust their water/nutrients for their plants....this is wrong , you do need to be correcting the ph for soil.

Peace Chronical.............