Let's talk about pH

Wed, 17 May 2017

Why pH is critical to get right in hydroponics?



You've probably heard the term pH (potential of Hydrogen) before and it's importance in hydroponics, read an article or two and come out more confused than before. Let's face it, not all of us did chemistry at school or remember the nitty gritty if we did. So. Let's try and keep this simple eh.

Plants get their nutrient (food) from the water we feed them, but they can only get all the right mix of nutrient if certain conditions are right.


Think of nutrients like a lock. pH is the key.

A major factor that affects food uptake is whether your solution is acid or alkaline.


We measure this in pH. A pH measurement can read between 1 and 14. Pure water is considered pH neutral or 7. Between 1 and 6.9 pH is considered acidic and between 7.1 and 14 water is considered alkaline. The ideal pH for most hydroponic gardening applications is between 5.8 and 6.3. If the pH of a solution is not within the correct range the plant will not have the ability to absorb some of the essential elements required for proper plant growth.  Believe it or not all plants have a particular pH range, which will produce healthy growth, and this level will vary from plant to plant, but most plants prefer a slightly acidic growing environment (5.8 to 6.3), although most plants can survive in an environment with pH values between 5.0 and 7.0.



Good question. By maintaining pH plants are less likely to suffer leaf problems or nutrient deficiencies and therefore you can expect plants to grow faster with bigger yields. Nutrients take on different forms (on a chemical level) depending on the pH around them. Some forms are easier for the roots to absorb than others. When the pH is too high or too low, the plant can show signs of a nutrient deficiency even when the nutrients are physically there at the roots.

With pH, you're helping plants get access to all the nutrients all the time. While pH is important for all grows, it is most important for growers using liquid nutrients. The way that liquid nutrients are formulated, they are highly available to plant roots, but only in the right pH range.

The way I see it, you spend good money on nutrients for your plants so you want them to have everything you give them so as to produce the results you want; tasty, healthy and colourful produce. If that means taking a little time to check the pH of your water and adjust it accordingly then that's time well spent, don't you think?



Essentially there are 2 simple methods of testing your pH levels which we explain below.

Method No 1: pH test kit with liquid drops.

This pH kit comes with a pH sensitive dye, a test tube and a colour chart. The test tube is filled with your water, a required number of drops of the dye are added and the water colour changes after a few minutes, which is then compared against the colour chart to determine the pH of the solution.

Method No 2: Digital pH meters.

The most high-tech method of checking the pH is with a digital meter.  All you have to do is dip the meter/electrode into your nutrient solution for a few moments and the pH value is shown on an LCD display.  The pH meters are fast and very accurate when properly calibrated.  These meters need to be cared for properly or they will no longer function.  The glass bulb electrode needs to be kept clean, and some are required to be kept lubricated at all times.  pH meters also need to be checked and calibrated frequently to insure accuracy.

These meters come in a huge array of sizes and prices. The most popular type of pH meter for the hydroponic gardener is the digital pen. These pens are manufactured by several different companies and are very handy and easy to use.



There are two common methods of watering plants in hydroponics. 

1.    The first is what is call run to waste. This passive way of growing often requires hand watering and the water that runs out is thrown on to the lawn or in the garden. Usually for this type of cultivation we would recommend that the grower makes up one large container of nutrient at a time. A 200 litre plastic drum is an ideal container. Once this is made up to the correct "strength" (conductivity), the pH can be checked and adjusted to the ideal level of 5.8-6.3. A careful note should be made of the exact amount of pH up or pH down that is added at this time. In future, this amount can be added as a routine when making up nutrient solutions, and pH should remain pretty constant from batch to batch, although spot checks are recommended from time to time. The nutrient solution in the tank should remain stable and can be applied to plants as needed.

2.    The second and more popular method is called recirculating. Recirculating hydroponic systems are ones in which the nutrient solution is supplied to the plants by a pump system. These systems include NFT (Nutrient Film Technique), Flood & Drain (or Ebb and Flow), Aeroponics, and DWC (Deep Water Culture) Systems. In most of these systems the nutrient solution is re-circulated to the roots over a period of time. In a recirculating system the pH will need checking and adjusting in the main tank on a regular basis. In most systems, fresh water is added to the tank to replace that used by the plants. The incoming water is usually of a higher pH than the nutrient solution, so there tends to be an upward drift in pH. This can be corrected by the regular addition of small amounts of pH down. This process of pH control can be carried out with pH kit with drops but as it needs doing often in this system, the busy grower would be better off using a meter. If you are feeding your plants from a recirculating nutrient tank, change the nutrient solution every 10 to 14 days and stop all nutrients 3 to 14 days before harvesting edible plants or fruits.



There are several chemicals used by the hobby gardener to adjust pH. The most popular are phosphoric acid (to lower pH) and potassium hydroxide (to raise pH). Both of these chemicals are relatively safe, although concentrated, they can cause burns and should never come in contact with the eyes or skin. Most hydroponic supply stores sell pH adjusters that are diluted to a level that is reasonably safe and easy to use. Concentrated adjusters can cause large pH changes and can make adjusting the pH very frustrating.

Several other chemicals can be used to adjust the pH of hydroponic nutrient solutions. Nitric acid and sulphuric acid can be used to lower pH but are much more dangerous than phosphoric acid. Food grade citric acid is sometimes used in organic gardening to lower pH.


Always add the nutrients to the water before checking and adjusting the pH of your solution. 


The fertilizer will usually lower the pH of the water due to its chemical makeup. After adding nutrient and mixing the solution, check the pH using whatever method you chose. If the pH needs to be adjusted, add the appropriate adjuster. Use small amounts of pH adjuster until you get familiar with the process. Recheck the pH and repeat the above steps until the pH level is where you want it to be. Once you have done this a few times, you'll nail it the first try. Beyond all the facts and figures, this critical step is truly simple and easy.

The pH of the nutrient solution will have a tendency to go up as the plants use the nutrients. As a result, the pH needs to be checked periodically and adjusted if necessary. To start out, I suggest that you check your pH on a daily basis. Each system will change pH at a different rate depending on a variety of factors. The type of growing medium used, weather, the kind of plants and even the age of the plants all effect the pH variations. There are several products on the market that you can use to quickly and easily adjust the pH in your hydroponic tank up or down as needed. We like to use pH up and pH down by Growth Technology.



Some hydroponic nutrients may become unavailable to the plant if the hydroponic nutrient solution pH drifts from an optimal reading, which for most plants is between 5.5 and 6.3. This condition is called nutrient lockout. If you regularly monitor the pH and the PPM (parts per million) of the hydroponic nutrient solution, you will have the ability to make corrections to your hydroponic solution for optimum plant growth. In order for your plants to feed from the nutrients you are adding they need to be dissolved in solution. Above pH 6.5 many nutrients and micro nutrients precipitate out of your solution and stick to the walls of the hydroponic reservoir. In the event of the nutrients precipitating out of the solution your plants are unable to absorb them and suffer nutrient deficiencies if not quickly corrected. You can improve nutrient uptake in your plants by using Humic and Fulvic acids. An unusually high pH will decrease the availability of Iron, Manganese, Boron, Copper, Zinc and Phosphorus. A pH that is too low will reduce the availability of Potassium, Sulphur, Calcium, Magnesium and Phosphorus. 



Milwaukee pH Digital Pen

This is one of the least expensive models by Milwaukee and it works great every time. It has a single calibration setting that makes it super easy to use. To check that the pH meter is calibrated correctly you just remove the black cap and put it in a little 7.00 pH calibration solution. If it reads 7.0 it is calibrated correctly and ready to use. It is very accurate at giving the pH readings in your hydroponic solution. You just turn it on, dip it into your hydroponic nutrient solution and stir. It has a range of 0.0 to 14.0. It has a very fast reading response and is very easy to use. It comes with its own batteries and they are supposed to last up to 700 hours. This little tool makes every hydroponic gardener's job much easier and is a must have tool.


Eutech pH Digital Pen

From the market leader of testers comes the EcoTestr pH 1 & pH 2 are a new range of value-for-money, quality pH tester series designed for fuss-free pH measurements. Accurate, and easy to use, these testers are ideal for quick pH checks in hydroponic gardening and aquaponics. The Eutech measures from 0.0 to 14.0, auto calibrates and has auto temperature compensation. Some of the nice features of this unit is that it is waterproof and floats if you accidentally drop it. It has a hold function that freezes the reading temporarily for ease of recording and has a clear cap that acts as a container for lubricating solution that keeps the bulb moist. 


Bluelab pH Pen

The ultimate handy solution for measuring pH and temperature!

The Bluelab pH Pen also measures the temperature of the solution, as root health is vital to the success of a crop. Temperature affects the growth rate and structure of a plant so a solution temperature of 18 - 22C is recommended. The hand held pH pen provides a compact quick and handy way to manage the success of your crop to ensure maximum uptake of nutrients. Teamed with our Bluelab EC pen and you have a handy, convenient and accurate system for ensuring optimum plant growth and health.


We hope you have found this article of some benefit. Please don't hesitate to contact us at Hydroponic Xpress if you have any questions.

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