pH is a scale used to measure the alkalinity or acidity of a solution. A reading of 7 indicates a neutral pH, with lower values being more acidic, and higher values being more alkaline. But how does pH impact hydroponic systems, and how can you guarantee that your nutrient solution remains at an optimal pH level?

Why Is pH So Important in Hydroponics?

As with all growing conditions, different plants have varying pH preferences. The majority thrive in a slightly acidic environment with the pH level between 5.6 and 6.2. However, most will survive adequately within a pH range of 5.0 and 7.5.

If the pH of the nutrient solution is outside the desired range, then the plants ability to absorb the nutrients will be hindered, resulting in stunted growth and nutritional deficiencies.

An overly acidic environment causes a calcium deficit which will injure the root system. Aluminium, hydrogen and manganese toxicity is also a possibility.

Conversely, in an alkaline environment, absorption of vital minerals such as iron, phosphorous and manganese is impeded, resulting in insufficient chlorophyll production which restricts growth and leads to poor yields.

Measuring pH

If anything has stuck with you from your old science classes, it is probably the BRA mnemonic (yes, we were all juvenile once!). Blue litmus turns Red in Acid. Litmus paper is the most inexpensive method of testing pH levels. The strip is dipped in the solution and then held against a colour chart to determine the pH reading. Unfortunately, the colour changes can be subtle, and given that a slight variance in pH can be detrimental to your crop, it’s not worth the risk.

Liquid kits are more expensive than litmus, but work on a similar principle. A few drops of the liquid tester are dropped into a sample of the nutrient solution, and the resulting colour change is compared to a chart. The colour change is a lot easier to read with this method.

Digital meters give the most accurate pH readings. Although they are more expensive than litmus and liquid testing kits, they can be reused again and again, meaning they are more economical in the long run. However, they are prone to electrode problems so a spare kit should be kept for emergency breakdowns.

Monitoring and Adjusting pH

To maintain optimal growing conditions, the pH of your solution should be checked regularly. Passive systems can get away with less frequent checks, but for active systems that use a pump, the levels should be checked daily.

If the pH is outside of the optimal range, it can be remedied easily by adding preformulated adjustors such as ‘pH UP’ and ‘pH DOWN’.

Hard Water

Hard water requires higher levels of acid to reduce the pH than soft water. If using phosphoric acid, it can lead to a build-up of phosphate in the tank. This causes nutrient imbalances and deficiencies. Using a nutrient solution properly formulated for hard water will prevent this. It’s worth investing in some hard water test strips before you begin growing.