Potential of Hydrogen

pH

Description
Used to specify the acidity or basicity of aqueous solutions. Acidic solutions (solutions with higher concentrations of hydrogen (H+) cations) are measured to have lower pH values than basic or alkaline solutions.
See Also
4.5–9 pH Test Strips
GH pH Up
GH pH Down
Liquid Culture Hydroponic System Operation
Precise Management of Hydroponic Nutrient Solution pH: The Effects of Minor pH Changes and MES Buffer Molarity on Lettuce Physiological Properties
Assets
Liquid Culture Hydroponic System Operation
Precise Management of Hydroponic Nutrient Solution pH The Effects of Minor pH Changes and MES Buffer Molarity on Lettuce Physiological Properties
Last Updated
2026-06-01
Reading Time
2 minute(s)
Word Count
313 words

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4.5–9 pH Test Strips
GH pH Up
GH pH Down
Liquid Culture Hydroponic System Operation
Precise Management of Hydroponic Nutrient Solution pH: The Effects of Minor pH Changes and MES Buffer Molarity on Lettuce Physiological Properties
Liquid Culture Hydroponic System Operation
Precise Management of Hydroponic Nutrient Solution pH The Effects of Minor pH Changes and MES Buffer Molarity on Lettuce Physiological Properties

The pH of the hydroponics reservoir should be between 5.5 and 6.5.

Optimum Water pH

Don't add the pH adjusting solution straight to the reservoir or you may shock the plant roots.

Add it to a gallon jug and let dilute for 5 minutes before slowing pouring the solution into your reservoir.

Adjusting pH Levels

pH should always be checked after getting the EC into the optimum range.1

pH and EC

Generally, fertilizer with Ammoniacal Nitrogen will tend to decrease pH, and fertilizer with Nitrate Nitrogen will tend to increase pH.2

Fertilizer on pH

pH Meter

Using a pH Meter

  1. Set the desired EC value of the solution.
  2. Calibrate the pH meter probe using the buffer solution. Make sure the nutrient solution is stirred up and allow the reading to stabilize, which may take a couple of minutes.
  3. If the pH reading is high, add phosphoric acid, citric acid, vinegar or pH down products slowly. Wait several minutes before adding more. Repeat until the pH reaches the optimum range.
  4. If the pH is low, add potassium hydroxide, potassium carbonate or a pH up product slowly. Repeat until the pH reaches the optimum range.
  5. Clean the probe and store in cleaning fluid.

Zeroing a pH Meter

There's a bottle of pH 7 solution.

Cleaning a pH Meter

Rinse with water. No soap is necessary.

If the pH is High (Lowering pH)
If the pH is Low (Raising pH)

  1. Electrical Conductivity and pH Guide for Hydroponics ↩

  2. Mattson, N., & Lieth, J. H. (2019). Liquid Culture Hydroponic System Operation. In Soilless Culture (pp. 567–585). Elsevier. https://doi.org/10.1016/B978-0-444-63696-6.00012-8 ↩