DIY pH Probe Calibration Solution

A while back I dropped my cheapo pH probe, and I had no calibration fluid handy.   ARGH!   What a pain!   I tried seeing if it was anywhere near correct…nope…my water tested at almost 9 instead of the typical 8.2.  So I did some research online (links below) to see if I could make my own solution since it was after fish store hours. What is boils down to is this…

1/2 tsp Borax (found in the laundry detergent aisle)
2 cups water (preferably RO/DI)

Mix the borax with the water.

Measure the temperature and compare the temperature and the pH probe’s value to the chart on the link (Table 2). Then…calibrate!

My pH probe should NOT have read 9.7. It should’ve read 9.2…so I had to calibrate it.

The Borax was $3.99 at Meijer…plus the cost of water. I can make 1,077 batches of calibration fluid. Boils down to less than a penny (compared to a couple dollars per commercially available solution).

Later, I checked this DIY calibration solution against a commercially available solution, thus giving this DIY solution credibility.  However, I would not use this solution for probes attached to a controller (most controllers assume the calibration fluid is at a set temperature).

If you don’t feel like buying 1000+ batches of this…give some away to other aquarists.  For more in-depth information on why this works so easily, see the links.


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  1. Adjusting Saltwater for a Water Change » Reef'd Up Aquatics

    […] At Step 14 we get into the more complicated testing.  First up is pH.  The easiest way to adjust this is to aerate the new saltwater for 24 hours beside the aquarium.  According to Dr. Randy Holmes-Farley, the target pH is 8.2, but an acceptable range is 7.8-8.5 (Link to his article on low pH).  I’d refer to his article for a more-than-detailed description on why pH is important to a reef tank.  Again, use the same measurement device for the aquarium as the new saltwater, and I recommend using a meter rather than a test kit due to accuracy issues.  Make sure the meter is calibrated, and if it is an inexpensive meter, you can calibrate it with this DIY pH Probe Calibration Solution. […]

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