Essentials – PH Pen

The pH levels in small hydroponic systems can often be overlooked if a grower is focusing more on monitoring a solution’s electrical conductivity or TDS level, balancing nutrients, providing beneficial additives and avoiding algae and plant pathogen problems.

However, overlooking pH control can be perilous for plants, particularly those that rely on water supplies with high alkalinity.

The pH of the nutrient solution is a major factor in determining the uptake rate of many essential nutrient ions.

Run pH too high and the dreaded nutrient lockout looms. Often, the first sign that pH has drifted out of range is a slight paling or yellowing of the younger foliage as the plants struggle to take up certain essential nutrients.

Many inexperienced growers tend to misinterpret this so a quick check of pH is always worthwhile when troubleshooting growth problems.

What is pH?

In simplest terms, pH is a measure of the acidity or alkalinity of a solution. The pH scale is logarithmic, which means a pH of 4 is 10 times more acidic than a pH of 5 and 100 times more acidic than a pH of 6. With a pH of 7 being neutral, such as with pure water, values below 7 are acidic and those above are alkaline (or basic).

Plants grown in hydroponics have a different optimal pH level than those grown in soil, so soilless gardeners need to be careful not to apply the pH recommendations for soil-grown crops to those they produce in hydroponics.

For most commonly grown hydroponic crops, an optimal pH range is between 5.5 and 6.5. Commercial growers often use a narrower range of 5.8 to 6 for most crops when they are using automatic controllers that regularly dose acid into recirculating systems to maintain this precise level.

The optimal acidic pH range for hydroponic crops is important as it affects the solubility, availability, and uptake of several of the essential plant nutrients.

What Causes pH Fluctuations in a Garden?

In a healthy, well-run hydroponic system, pH fluctuations are normal and in some instances, such as recirculating nutrient film technique with a large crop of mature plants and small nutrient volume, pH changes can be quite rapid and require frequent adjustments to stay within a narrow range for optimal nutrient uptake.

As plants remove nutrient ions from the solution, the solution’s pH drifts up or down. If left uncontrolled, the pH will often drift downwards for several days after planting a new crop, after which the pH will steadily increase.

This is due to the differential uptake of ions from the solution, with the release of hydrogen (H+) or hydroxyl (OH-) ions from the root system.

As positive ions such as cations Ca2+, K+, Mg2+ are removed from the solution, hydrogen ions (H+) are released from the root system to equalize the ratio of anions to cations in the root zone and this lowers the pH of the solution.

When the crop begins an active growth phase, anions such as NO3 are taken up, which increases the pH through the release of hydroxyl ions (OH-) into solution.

Once plants are well established, most hydroponic systems tend to see a gradual and continual increase in pH over time, which is countered with doses of diluted acid.

Water Supply and Water Treatment for pH

Many of the pH problems that growers encounter originate from the water supply. Many sources of water, including the city supply, can have issues with alkalinity and while that is not a problem for human consumption, it can cause problems in a hydroponic system.

The alkalinity of a water supply describes the strength of a high pH so a water supply with a high starting pH and high alkalinity takes a far greater volume of acid to bring it down to optimal levels than a water supply with low alkalinity and of the same pH.

Alkalinity is usually provided on water analysis reports from city supplies and is worth checking if continual pH rises requiring large doses of acid is a problem.

High alkalinity is considered greater than 300 mg/L of calcium carbonate and low alkalinity is less than 100 mg/L. When high-alkaline water is first added to the nutrient reservoir, it can take large volumes of acid (pH down solution) added over a number of days to finally bring down and stabilize the pH in the 5.8 to 6 range.

However, adding large amounts of acid is not only time-consuming in terms of monitoring, adjusting and readjusting, but it can also create imbalances in the nutrient ratio as acids also add in nutrient ions.

Nitric, phosphoric and sulphuric acid all add N, P or S to the carefully balanced nutrient solution, so accumulation can occur. Growers with a water supply of high alkalinity can prevent this issue by pre-acidifying the source water down to a pH of 6 before using it to make up nutrient solutions or adding as top-up water to a nutrient reservoir.

Once the water supply has been stabilized at a pH of 6 and the alkalinity countered to the point, it remains at that pH for 24 hours and can be used in the hydroponic system. Much less acid will then be required for pH control.

Hydroponic Nutrient Formulation and pH
Nutrient formulations or products all have different starting pH values because individual salts become more or less acidic when dissolved into water. Salts such as monopotassium phosphate lower the pH more than salts such as calcium nitrate. Most formulations will result in an initial pH of around 5.5 to 6, which is ideal for the growth of hydroponic crops.

In hydroponic solutions, some salts can be used to influence the pH control of the nutrient solution, reducing the requirement for acids during growth development phases of the crop.

Ammonium nitrate is one salt used for this purpose, and the optimal amount is that which provides 10 to 15% of the total nitrogen of the formula in the ammonium form.

Ammonium in nutrient solutions tends to be acidifying because, unlike nitrate, it is a positive ion, and when taken up by plants it is replaced by hydrogen ions, reducing pH in the root zone. In addition, ammonium forms ammonium hydroxide and hydrogen ions that produce a mild acidifying effect when in solution.

Many of the nutrient products on the market designed for hard or alkaline water sources use a certain percentage of ammonium nitrate to help counter pH increase.

While this is effective in keeping pH levels down, the ammonium form of nitrogen can cause growth issues and even toxicity if the percentage used is too high and under certain growing conditions.

Ammonium competes for calcium uptake, so only small levels—10 to 15% of total nitrogen—of ammonium as a nitrogen source are recommended for most crops and well-formulated nutrient products usually contain less than this.

Essentials – a brand by GHE.

We share your passion for plants — that’s how we got our start, and that’s what keeps driving us forward.

Over 40 years ago, an inspired group of scientists, engineers and technicians came together with an ambitious goal: to advance agricultural quality and innovation through the use of key manufacturing processes and cutting-edge research.

They succeeded. But it was only the beginning.

In launching General Hydroponics, that team created a foundation that’s allowed us to expand in meaningful and industry-changing directions. We now have state-of-the-art facilities in North America and Europe where researchers develop products, solutions, and systems that help you care for your plants in a way that delivers the best possible results.

Our Santa Rosa, Calif., factory features large on-site grow facilities that use alternative energy sources and green technologies to save water and power. A specialized farm division has tested over 100 plant varieties for yield, flavor, nutrition, appearance, disease resistance, growth rate and suitability for hydroponic systems.

While improving our customers’ growing practices, we’re also dedicated to creating a cleaner and more environmentally efficient world. That’s why we offer advanced systems powered by solar energy, as well as filtration products that make the most of organic components and nutrient formulations. With industry-leading manufacturing and research, we continually develop products that enhance your results while being kind to the environment.

We honor the vision of our founders by always thinking about what’s next. With consistent quality, value and results, General Hydroponics remains committed to leading the industry, offering the most innovative products available and serving growers like you around the world.