What is pH

This is a subject my high school teacher quickly covered as:

"It is a logarithmic representation of the concentration of H+ ions

The pH scale measures how acidic or basic a substance is

pH==7  neutral

pH<7  alkaline [basic]

pH>7  acids"


This didnt make sense at the time, a magic concentration of H+ ions [pH7] is neutral but any fewer or any more and it is not neutral, but the reason why this occurs s quite a hard concept to understand, if you want to understand it see reference [1]


Why is pH important in Hydroponics

The availability of chemicals to the roots is heavily dependant on pH[see figure below]. In short, get the pH major wrong and your plant wont be able to use the expensive nutrients in the growing fluid you just made.


[Nutrient availability vs pH,  thicker lines is better][2]

If you have ill plants, pH is a hard one to find as the issue because it will usually appear to be a deficiency of P. making you believe that you need more P [Phosphorous], when in fact you just need to change the PH to make more P available to the plant.


What is the "Best" pH

This is a hard one to  pinpoint, it depends on the types of plants in the system and has to accommodate any other living organisms in the system [fish].

It is commonly quoted that a pH of 5.4 to 6.4 is the best range for most plants [2][3]

That is why we will have a set point of 5.9 for our pH controllers in many hydroponics/aquaponics.


Please do check that your fish are happy with this pH and consider researching the optimum pH for the plants in your system.



[1]Determining and Calculating pH - Chemwiki

[2] Bodie V. Pennis " Essential pH Management in Greenhouse Crops: pH and Plant Nutrition" B 1256

[3]A Publication of the International Plant Nutrition Institute (IPNI) "SOIL PH AND THE AVAILABILITY OF PLANT NUTRIENTS"