Measure the Nutrient Concentration
Familiarize yourself with your EC meter. An EC meter measures the electrical conductivity in the solution. This tells you how much of the nutrients are present in the water.
Insert the EC meter's probe into your garden's nutrient solution to take a base reading. Compare this reading to a chart of ideal EC readings for the plants you are growing. Many EC meters intended for hydroponics come with this chart (or see Resources section).
If the EC reading is too high, add water to your nutrient reservoir. This will dilute the solution. If the EC reading is too low, add concentrated nutrient solution to the reservoir. Mix well and let the solution rest for 10 minutes, then re-test. Repeat this step until EC levels are within acceptable ranges, as indicated by your ideal readings chart.
Measure the pH of Your Nutrient Solution
Familiarize yourself with your pH meter and calibrate it according to manufacturer's instructions.
Dip the pH meter probe into the nutrient solution and record the results. If you suspect the readings are inaccurate, use pH strips or a liquid test kit to confirm your results. For most plants, the ideal pH is between 6.0 and 6.5.
If the solution is to acidic (the pH is too low), add one to three drops of phosphoric acid to the nutrient reservoir. If the solution is too basic (the pH is too high), add one to three drops of potassium hydroxide. Mix well and let the solution rest for 10 minutes, then re-test. Continue to adjust until the pH is between 6.0 and 6.5.
Re-check the EC and pH levels of your nutrient solution every three to five days to maintain ideal conditions for your plants. If you suspect growth problems, check and adjust more frequently.