When customers experience issues with our pH test strips, we often look to the solutions they’re testing as one possible cause.

The majority of our pH test strips are designed for use in aqueous (water-based) solutions. Our test strips use a visual color matching system (matching the test pad to a color chart) to determine the pH of the test solution.

The colors used on our pH color charts have been developed using solutions that contain typical ionic strength and buffering capacity. When problems arise in measuring pH, it’s usually because the solution has low ionic strength and/or buffering capacity.

The chemistry that takes place on the pH test pad requires the presence of ions in the test solution. Low ionic strength or poorly buffered solutions, such as distilled water, RO water and soft water don’t have enough ions for the chemistry to work correctly. This is a common problem with pH probes and instruments, but it’s also a problem with test strips, although to a lesser extent.

Adjusting for Low Ionic Strength / Buffer Capacity

In many cases of low ionic strength or buffering capacity, the test pad will develop color, however, it can take up to 1 minute for the chemistry on the test pad to do its job. If you suspect you have low ionic strength or buffering capacity, leave the test pad immersed in the solution for an extended time.

You can also try increasing the ionic strength of the solution by adding a neutral salt (sodium chloride or potassium chloride). These salts will not affect pH, but they will increase ionic strength.

On the other hand, adding materials such as bicarbonate, citric acid or phosphates will improve the buffer capacity but will also significantly impact the pH of the test solution. You’ll get an inaccurate measurement if you add any of these materials.

Testing Aquariums, Pools & Spas

testing pH, aquarium pH, pool pH, spa pH

 

There are pH test strips specific to testing aquariums (salt or freshwater) or pool/spa applications. These strips are designed to account for the finely balanced water chemistry required and the biological load present in these waters. Standard pH test strips may not work properly.  Be sure to use pH test strips designed specifically for an aquarium or pool/spa.

Our pH test strips are deceptively intricate with their finely balanced formulas. It’s important to understand how the solution being tested can impact the result. Selecting the right test strip for your application is critical to obtaining accurate measurements. If you’re uncertain about which test strip to use for your application, contact us and we’ll help get you on the right track.