Question: How do I use pH strips to test pH?

warren is asking a question about water-quality
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by warren | February 28, 2018 18:19 | #15837

I'm sure there are lots of guides out there. What are some minimal step-by-step instructions (ideally with illustrations or photos!) to guide people using pH strips? Thanks!!


You want to check the expiration date of the strips, first. If they are expired, throw them out. And beware. If you are using something like red and blue litmus paper, red litmus paper will eventually turn blue and blue litmus will eventually turn red. So check the labels.

First, put the pH strips on something like a Petri dish or beaker cover, preferably on top of a white piece of paper. Then take a glass stirring rod ( alternate- plastic disposable pipette), put it in the solution to be tested, and then to lift a drop out of solution and put it on the pH paper. Then rinse the stirring rod with di water. This avoids contaminating the tested solution with the dye used in the test strips.

A word of warning. Ph test strips can be wrong. You can get oxidation occurring that will mask the pH.

Thanks, especially for the tips on oxidation! What can cause that, and how might it be avoided?

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Hi @Ag8n , does "di water" mean distilled water? Also, i see @warren asked a sort of follow-up that seems to be about storing pH strips and keeping them dry, I thought you might have input on that. thanks!

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In this area (Ohio), at least, trace levels of hypochlorite ( bleach) work their way into the storm sewer. If you have a piece of red pH paper, bleach acts like it would on red shirts. It turns it pink. That causes an error in the pH reading. We would double check with a pH meter when something seemed wrong and eventually traced it to hypochlorite. It didn't take much ppm. The new pH paper might be better than what I used. So please see how your results track now.

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