pH test kits are an important tool for all aquarists, especially reef-keepers.
Everyone uses them, but aquarists often wonder if the results are accurate. Are more expensive test kits better than lower-priced options?
Online discussions of pH test kits can bring out strong opinions, mostly based on emotions. pH test kit evaluations based on comparing two or more kits on an aquarium water sample is not valid. That’s because you don’t know what the true pH of the water is. One of the two kits may be accurate or both kits could be wrong. You must first know the baseline pH of the water, then compare test kit results.
But there’s more!
Based on 30 years of developing test methods, I’ve found if someone knows what the test kit reading should be, they’ll usually see that result. But given the same water sample, with no knowledge of its pH, they’ll see a different result. There can be a subconscious bias toward a favorite brand of kit and the desire to see the “right result.”
For our test kit evaluation, we used a “blind” test panel of three persons. We knew what the pH levels were in the water samples, but the observers didn’t. They simply performed the tests and wrote down the results.
How pH test kits work
pH test kits use one or more pH-sensitive dyes. The dyes respond to pH levels by changing color. The goal of the test kit designer is to select dyes that show distinct colors at the desired pH ranges.
Everyone would love to have a pH kit that was yellow at 8.0, green at 8.1, red at 8.2 and so on. But that’s not possible because there are no dyes that can create those dramatic and distinct colors for such a narrow pH range. So, the best we can do is have a color gradient in the narrow saltwater pH range.
The next component is the color chart. The color chart must closely match the colors of the solution in the test vial. Ideally the colors for the pH chart are selected using ink color swatches under proper lighting. The industry standard for printing, packaging and graphic arts is viewing under 5000K lighting. This lighting standard will provide the most “honest” color rendition and is the gold standard for color matching. Once the ink colors are selected, they’re printed on paper pH comparison charts. Improper lighting at home can make comparing the pH test results difficult. Aquarium and ambient room lighting can affect how we see colors on paper and through test vials.
For our test, we used a 5000K light box so everyone on the panel saw the pH test results under the same ideal lighting conditions.
How the test was performed
For the comparison we selected pH test kits from Giesmann, Salifert, API and Seachem. A hand-held Hanna pH meter was also included in the line-up. Each of the panelists independently performed pH tests on three water samples, using each of the pH test kits and meter. The pH of the water samples was confirmed using a calibrated laboratory pH meter. The tests were performed using the manufacturer’s instructions. The Hanna pH meter was calibrated using the supplied calibration solutions. pH kit readings were made in the light box.
When the results were tallied we were surprised that all three panelists came up with the same pH readings for all the kits. Each panelist kept their test results private. There was no discussion between panelists during the tests. The uniformity of the panelists’ results indicates that each test kit provided consistent results. In some cases, panelists felt the color in the test vial was somewhere in between two pH levels. This is indicated on the results chart.
|pH 7.88||pH 8.05||pH 8.40|
*Panelists felt the pH was in between two pH levels
All the pH test kits produced consistent measurements based on the panel’s unbiased, independent observations. The big surprise was the performance of the Pocket pH Tester HI98108 pHep+. Hand-held pH meters are notoriously inaccurate compared to more expensive professional models. The Hanna pH meter consistently provided a level of accuracy we’ve not seen with other low-cost meters.
pH test kits are fast and easy, providing an economical way to keep a close watch on your tank’s pH. The Hanna pH meter eliminates the variables associated with color matching, which can be affected by room lighting and slight color blindness, but you’ll have to calibrate the meter every time you want to measure pH.