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pH Meters and Calibration

pH plays a critical role for reef keepers. Reef tanks must have a stable pH environment to sustain life and flourish. Fluctuating pH levels can wreak havoc on reef tanks causing poor coral growth which can result in death. The pH level in a reef tank typically ranges between 7.9 and 8.4 with optimal levels of 8.2 to 8.4. However the pH in a hobbyist reef tank tends to be on the low side of this range due to reasons that may include but are not limited to calcium carbonate reactors, large bioloads (over stocking) or over feeding to name a few. So it is essential for an aquarist to be able to accurately determine the pH of his or her system.

Pinpoint pH Controller
$199.00

One of the fastest and easiest ways to determine pH is by using a pH meter. There are many different types of pH meters available to the hobbyist. The price of these meters can range between $80.00 to well over $1000.00. Luckily for us, an $80.00 pH meter will work just fine.

When measuring pH, it is essential to understand the instrument and how an accurate pH reading can be measured. When using a pH meter for the first time it a necessary to calibrate the unit before use. This only takes moments and will help produce accurate results. The items required to calibrate a meter are calibration fluids with the known pH levels of 4.0, 7.0, and 10.0 as well as RO/DI water and a thermometer.

It is necessary to know the temperature of the liquids that are going to be measured. Once that is determined the temperature setting on the pH meter should be set to that temperature. The probe is then inserted into the neutral calibration standard of pH 7.0. The calibration standard should be agitated gently while the probe is measuring the pH. Once a stable pH reading has been obtained it may be necessary to adjust the pH meter to correct the actual reading to 7.0 using the calibration dial.

The probe is then removed from the 7.0 calibration fluid and rinsed thoroughly with RO/DI water. The probe is then inserted into either the 4.0 or 10.0 calibration standard. This is determined by the expected pH of the test sample and the opposite expected pH standard will be measured first for calibration. For example in a reef tank the sample water will typically be between a pH of 7.9 to 8.4 which is basic. The correct order of calibration would be to measure the acid calibration standard of 4.0 using a gently swirling motion, once a stable reading is obtained the pH meter should be adjusted using the 4/10 calibration dial to read 4.0. The probe is then rinsed with RO/DI water and then the calibration method is repeated with the basic or 10.0 calibration standard.

This way the pH meter will have a calibration curve to provide accurate pH readings at basic pH levels. If one were to measure acidic liquids the order in which the calibration liquids would be reversed so that the 4.0 pH liquid would be measured last. Keep in mind that the 7.0 pH calibration liquid is always measured first.