Hydroponics is a method of cultivation where plants are grown without soil, relying entirely on a water-based nutrient solution for all their sustenance. Since plants cannot extract nutrients from a soil medium, the grower must precisely manage the composition and balance of the water provided. Consistent testing ensures the plant’s changing needs are met and prevents imbalances that can lead to deficiency or toxicity.
Essential Parameters and Measurement Devices
The two primary parameters requiring constant monitoring in a hydroponic system are Electrical Conductivity (EC) and pH. EC measures the overall concentration of dissolved mineral salts within the solution, serving as a reliable indicator of nutrient strength. This measurement is typically expressed in units of millisiemens per centimeter (mS/cm). Growers use a dedicated EC meter or a combination meter to obtain this figure.
Total Dissolved Solids (TDS), sometimes expressed as parts per million (PPM), is calculated from the EC reading. Because the conversion factor used to calculate PPM can vary between meters, EC is generally considered the more consistent standard for measuring nutrient concentration.
The second parameter, pH, measures the acidity or alkalinity of the solution on a scale of 0 to 14. This reading controls the availability of nutrients to the plant roots. If the pH drifts too high or too low, certain elements become chemically locked out and unavailable for absorption. A digital pH meter provides the most accurate reading, though less expensive test strips or liquid drop kits are also available.
Step-by-Step Procedure for Accurate Testing
Before taking any measurement, ensure the nutrient reservoir has been thoroughly mixed and circulating. This guarantees the sample is representative of the entire body of water. Taking the reading at the same time each day helps establish a consistent baseline for tracking trends.
Maintaining the accuracy of digital meters requires regular calibration using specialized buffer solutions of known values. For a pH meter, this involves dipping the probe into two or three different buffer solutions (e.g., pH 7.0 and pH 4.0) and adjusting the meter to match the known value. EC meters are calibrated with a single solution of known conductivity, a process that should be repeated weekly or bi-weekly.
When taking a measurement, the probe should first be rinsed with distilled water to remove any residue. The clean probe is then submerged into the nutrient solution, and the grower waits for the reading to stabilize. Since Electrical Conductivity is temperature-dependent, many modern EC meters feature Automatic Temperature Compensation (ATC) to correct the reading.
The temperature of the solution itself is also a factor, with an optimal root zone range between 18 and 22 degrees Celsius (65 to 72 degrees Fahrenheit) for effective nutrient uptake. After testing, the probes must be cleaned again and stored according to the manufacturer’s instructions to prevent sensor damage.
Interpreting Readings and Adjusting the Nutrient Solution
Once measurements are taken, the numbers must be compared against the needs of the specific crop and its growth stage. The acceptable EC range for most hydroponic plants falls between 1.2 and 2.0 mS/cm, though seedlings require lower concentrations. If the EC reading is too low, concentrated nutrients must be added gradually.
To increase the EC, the grower mixes a small amount of nutrient concentrate into water before slowly introducing it to the reservoir. If the EC is too high, indicating an overly concentrated solution, fresh water must be added to dilute the mixture. Dilution requires adding water, mixing thoroughly, and retesting until the reading falls back within the target range.
The pH reading should be maintained within the slightly acidic range of 5.5 to 6.5 for the majority of hydroponic crops. This narrow window facilitates the maximum solubility and absorption of all necessary macro and micronutrients.
If the pH is high (alkaline), a “pH Down” product, commonly containing phosphoric acid, is used to lower the value. Conversely, if the pH is low (acidic), a “pH Up” solution, such as potassium hydroxide, is introduced to raise the value.
Adjustments must be made slowly by adding a very small, measured amount of the adjuster solution, stirring the reservoir, and then retesting. This careful, iterative process prevents sudden, large swings in pH that can stress the plants and destabilize the solution.