When you are growing hydroponically checking and adjusting pH is a simple matter. It can be a bit more complicated when growing organically or in the soil. There are several ways to check the pH of the nutrient solution in your hydroponic system.
Paper test strips are probably the most inexpensive way to check the pH of the nutrient solution. These paper strips are impregnated with a pH sensitive dye which changes color when dipped into the nutrient solution. The paper strip is then compared to a color chart to determine the pH level of the solution is checked. These test strips are inexpensive, but they can be hard to read because the colors differences are subtle.
Liquid pH test kits are probably the most popular method to check pH for the hobby gardener. These liquid test kits work by adding a few drops of a pH-sensitive dye to a small amount of the nutrient solution and then comparing the color of the resulting liquid with a color chart. While slightly more expensive than the paper test strips, they are easier to read and extremely accurate and reliable.
The Most high-tech way to check pH is to use the digital meters. These meters come in a huge array of sizes and prices. The most popular type of pH meter for the hobby gardener is the digital pen. These pens are manufactured by several different companies and are very handy and easy to use. You simply dip the electrode into the nutrient solution for a few moments and the pH value is displayed on an LCD screen.
The pH meters are very accurate (when properly calibrated) and fast. They need to care for properly, however, or they will quit working. The glass bulb electrode must be kept clean and some are required to be wet at all times. The pH meters are actually very sensitive volt meters and are susceptible to problems with the electrode.
The pH meters are slightly temperature sensitive. Many of the pH meters on the market have Automatic Temperature Compensation (ATC), which corrects the reading with respect to temperature. On meters, without ATC the pH should be checked at the same time of day each time in order to minimize any temperature-related fluctuations.
The pH meters usually need to be calibrated frequently, as the meters can drift and insure accuracy you must check calibration often. With most pens, the tip needs to be stored in an electrode storage solution or in a buffer solution and should never be allowed to dry out.
Due to the fact that pH meters have a reputation of breaking down without warning it is a good idea to keep an emergency backup for checking pH (paper test strips or a liquid pH test kit), just in case.