How To: Calibrate a pH Meter

Electronic pH meters are very important tool for hydroponic gardening because it will simply and accurately test your pH to ensure your plants are given nutrients at a safe and healthy range. Depending on how often you pH your nutrient solution, it will need to be calibrated accordingly. If you use your pH meter daily, you will need to calibrate it about once per week; if you use your pH meter once a week, you can get by with calibrating it once a month. There are a variety of pH testers available on the market, and each has slightly different calibration methods so make sure to check the user's manual first for instructions. To prepare for most calibrations you will need the following items:

-7.0 Calibration Solution
-4.01 Calibration Solution
-3 Small Cups
-Small Screw Drive (Varies Depending on Model)
-Distilled or Reverse Osmosis Water

Most meters will require that you use two different solutions to balance out the meter's calibration, a 7.0 and a 4.01 solution. These solutions are to be used as a buffer because they are pre-calibrated to always have the pH level that is printed on the label. First, pour a small amount of each calibration solution into separate cups (enough to cover the electrode) and distilled or reverse osmosis water into a third cup. To start out, you should rinse the pH electrode with distilled or reverse osmosis water to ensure that there are no contaminants that will interfere with a proper pH reading. There should be no buildup or cracks on the electrode when you examine it. After you have dried off any excess water from rinsing the electrode, you can place the electrode directly into the 7.0 solution and allow the reading to settle; this should take less than a minute. Some meters require that you press and hold the "MODE" button or "SET/HOLD" button on your meter first. For these meters, a "CAL" icon will likely appear and allow you to place the electrode in the 7.0 solution. Once the reading has settled, the meter will either auto-adjust or will require an adjustment of a small screw to make the reading match the pH of the calibrating solution.

Next, you will rinse the electrode in the purified water to clean off any excess 7.0 calibration solution. Dry off the excess water and place the meter into the 4.01 calibration solution. Again, your meter may automatically prompt you to submerge the electrode in the 4.01 solution, or may require you to press and hold a "MODE" or "SET" button. Allow the reading to settle and the meter will either auto adjust or will require the manual adjustment of a small screw to match the 4.01 solution. Now you have calibrated your meter! Congratulations!

Remember to always pour the calibrating solution into a separate container for each use. Never pour used solution back into the unused container because this may cause contamination. Also make sure that when you are finished calibrating the electrode, you rinse it in purified water and store the electrode moistened. Never store your electrode dry. Happy pH testing!