pH Controller and Calibration Question

[Steve Erekson]

I purchased a used Reef Fanatics pH controller for a very low price off a local hobbyist recently, hoping I would be able to put it to use on my nano as a way to prevent accidental kalk overdoses. My issue is this pH controller was designed for calcium reactor use and therefore only has calibration points at 4.0 and 7.0 pH and does not have the ability to calibrate it at 10.0, which is more in line with the range I need. I have two questions:

1) Will it really make a huge difference to the accuracy in the 7.8 - 8.2 range if it does not have a calibration point at 10.0?
2) If so, could I potentially use a 7.0 calibration solution for the 4.0 point and a 10.0 solution for the 7.0 point and simply take any reading and subtract 3? I know pH is logarithmic and not linear so I have no idea if this is a good idea or not.

Appreciate any input.

 

[Randy Holmes-Farley Verified Community Expert]

I purchased a used Reef Fanatics pH controller for a very low price off a local hobbyist recently, hoping I would be able to put it to use on my nano as a way to prevent accidental kalk overdoses. My issue is this pH controller was designed for calcium reactor use and therefore only has calibration points at 4.0 and 7.0 pH and does not have the ability to calibrate it at 10.0, which is more in line with the range I need. I have two questions:

1) Will it really make a huge difference to the accuracy in the 7.8 - 8.2 range if it does not have a calibration point at 10.0?
2) If so, could I potentially use a 7.0 calibration solution for the 4.0 point and a 10.0 solution for the 7.0 point and simply take any reading and subtract 3? I know pH is logarithmic and not linear so I have no idea if this is a good idea or not.

Appreciate any input.

It is OK to calibrate at pH 4 and 7 for use in seawater. I wouldn't do strange things like tricking the device about what the pH is. lol

I discuss such issues here:

Aquarium Chemistry: Measuring pH with a Meter

This article describes how pH meters work, how to select one to use, and how to best use it to measure the pH of a reef aquarium.

reefs.com

It is clear that with similar errors in the standard solutions, the errors in the measurements at pH 8-10 are smaller when calibrating at pH 7 and 10 than at pH 4 and 7. Whether these differences are important depend on the application and expectations of the aquarist.

 

[SteveMM62Reef]

I’ve calibrated my Pinpoint with 7.0 or 10.0 with no problem. I took a Fine Tip Paint Marker, and marked the direction to turn the Screws to increase the reading. After I’ve calibrated it, I use two different test kits, and zero it in on the tanks, actual pH. Afterwards I generally Calibrate it off the tanks pH, unless something seems seriously wrong. IE Time for a new probe. Don’t forget to clean the Probe with a Soft Toothbrush.

 

[Steve Erekson]

It is OK to calibrate at pH 4 and 7 for use in seawater. I wouldn't do strange things like tricking the device about what the pH is. lol

I discuss such issues here:

Aquarium Chemistry: Measuring pH with a Meter

This article describes how pH meters work, how to select one to use, and how to best use it to measure the pH of a reef aquarium.

reefs.com

It is clear that with similar errors in the standard solutions, the errors in the measurements at pH 8-10 are smaller when calibrating at pH 7 and 10 than at pH 4 and 7. Whether these differences are important depend on the application and expectations of the aquarist.

I appreciate the insight. The application is pretty basic, if pH goes above a set point, turn off the ATO pump. It's just a backup system in case of a stuck ATO sensor to prevent kalk overdoses. Sounds like I'm overthinking it as usual, I'll just roll with the 4 and 7.