pH Calibration

pH n : p(otential of) H(ydrogen); the logarithm of the reciprocal of hydrogen-ion concentration in gram atoms per liter; used as a measure of the acidity or alkalinity of a solution on a scale of 0-14 (where 7 is neutral)

Most people are familiar with pH("potential hydrogen") as an indicator of how acid or alkaline asolution is. The pH scale ranges from 0 pH (very acidic) to 14 pH (highlyalkaline). Pure water, at 7 pH, is neutral--neither acidic or alkaline.Maintaining proper pH is critical, whether growing in soil or hydroponically.Plants absorb each nutrient element only within a certain pH range, and becausethis range is different for different nutrients, there is only a relativelysmall pH range in which all nutrients are available.

Plants can generally survive within a pHrange of 5.0 - 7.5. Below 5.0 pH there is a danger of burning and destroying thesensitive root tissues, while at pH levels of 7.0 and above some nutrients mayprecipitate out of solution and become unavailable to the plants. The optimumlevel is about 6.3 or 6.5 pH, with anything in the range of 6.0 - 7.0 beingacceptable. Unless an automated controller is being used, the pH level should bemanually tested and corrected daily.

The natural tendency in hydroponicssystems is for the pH level to rise as plants use up nutrient. This must becorrected by use of an adjusting "pH down" (acidic) solution. Thereare also alkali, or "pH up" solutions available to correct a pH levelthat has become too low. An adjusting solution (either acid or alkali) shouldnot be introduced into the system at full strength because this can lock up(precipitate) nutrients, in addition to being a shock to the system. Ideally,the adjuster should be diluted to about 0.001 strength (0.1% solution) before itis introduced into the system. For example, if you begin with "fullstrength" (75% solution) of phosphoric acid, you should dilute one partacid to about 750 parts of fresh water. Similarly, acid (or alkali) at 8%strength would ideally be diluted one part adjuster to 80 parts fresh water.

More and more growers are usingelectronic pH meters to measure their pH. All pH meters are very sensitive andsubject to variations in measurements due to a variety of factors. This meansthat all pH meters periodically need to be re-calibrated. Evolution Solution pHCalibration Solution is a precision crafted solution that is available in pH4and pH7 levels. It is best to calibrate your meter using both pH4 and pH7 as atwo-step calibration process.

Evolution Solution pH CalibrationSolution is available from your favorite hydroponics retailer in the followingsizes:

CROP	pH
Beans	6.0-6.5
Beetroot	6.0-6.5
Broccoli	6.0-6.5
Cabbage	6.0-6.5
Capsicum (peppers)	6.0-6.5
Cauliflower	6.0-6.5
Cucumber	6.0-6.5
Lettuce	6.0-6.5
Pea	6.0-6.5
Pumpkin	6.0-6.5
Spinach	6.0-6.5
Squash	6.0-6.5
Strawberry	6.0-6.5
Tomato	6.0-6.5