So what is pH...

and why is measuring it so important?

pH is the measurement of acidity and its opposite, alkalinity in a solution. Neutral pH is 7.0 pH. Acidity measures below seven pH (7.0pH) with alkalinity measuring above it (7.0pH).

It is important to maintain a hydroponic nutrient solution at a pH level where the elements in the nutrient solution are consistently available to the plant. If the solution is too acidic or too alkaline it can cause “lock up” – a situation which restricts certain elements essential for growth from being absorbed by the root structure.

Deficiencies in the required elements become apparent in the plants growth and can lead to crop failure.  Additionally the pH of the water we drink is crucial to our health, the pH of a swimming pool is important, not only for our skin and eyes, but also for the efficiencies of sanitizers and pool equipment. Again the pH of the water a fish lives and breeds in is critical to its existence as certain species require a particular pH to survive.

The elements we add to a solution will either increase or decrease the solutions pH measurement. Only accurate measurement of the pH level will allow complete control of the outcome. 
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What is the preferred pH range for your plants?
Mastering pH with Bluelab

When the pH is slightly acidic most nutrient elements are available to a plant.

Slightly acidic range:

Hydroponic solutions: between 5.5 pH and 6.3 pH
Soil crops: between 6.2 pH and 7.2 pH

Individual crops have their own preference for pH values. That is, they do best at certain pH levels.

Whatever food solution you use, keep your pH in a fairly tight band. Consistent balance gives consistent growth.

It’s not just the nutrient mix... it’s the right pH that delivers the food. 

Accurate pH readings in solutions with a ppm (500 Scale) of less than 250ppm [0.5 EC] can be challenging to obtain, and require the pH probe to be extremely well maintained and in excellent condition. For this reason Bluelab recommend that for general applications the ppm of the solution being measured should be greater than 250ppm (500 scale). If pH measurements in solutions of less than 250ppm are required then Bluelab recommend that guild lines for measuring pH in low ionic strength solutions be followed.
Choosing a Bluelab pH meter
Bluelab has a range of products suitable for measuring the pH in nutrient solution or soils. Have a look at the range by application (intended use) or view the pH pen, soil pH penpH meter and soil pH meter to see which might be best for you.

If you'd like an instrument that measures pH, ppm/EC (conductivity) and temperature, try the Combo Meter, Guardian Monitor or a Dosetronic Controller.