Cleaning and Calibrating pH Electrodes

Introduction
Cleaning the pH Electrode
Calibrating the pH Electrode

Introduction

pH electrodes are very sensitive pieces of equipment. They can easlily be damaged. Because good electrodes are expensive you should really pay careful attention, not only to how you handle them, but also to how you clean and recalibrate t hem. Here are some of the areas to pay attention to when using such electrodes:

Do not submerse the electrode completely in the water
Make sure you have removed the protective cap, carefully
Do not discard the cap, you may need it later
Be very careful not to damage the glass bulb tip at the sensing end of the electrode
Surrounding the sensing tip is a so-called "junction". Be careful not to damage that either when you handle the probe.
Always turn your meter off before disconnecting the electrode
Ground your tank. See another document in the library to find out how to do so.
Do not touch the sensing end of the electrode with your fingers
Do not touch the sensing end of the electrode with anything that is hard or rough
The glass tip scratches easily and false readings will occur when this has happened
Always place the electrode in an areas with constant current
Current needs to move over the junction and the glass tip
Be careful not to knick or damage the lead
Do not run the lead next to an electrical wire (e.g. a cord or extension cord)

Cleaning the Electrode

As time goes on, the tip of the electrode (the portion that is in the water) will tend to pick up and trap dirt. The glass sensor may even get coated with algae, calcium carbonate, lime, etc. When this happens you are, obviously, not going to obtain an accurate reading! Since the water cannot come in full contact will all the sensing parts the reading you obtain will be erroneous. Keep that in mind. Probes need to be cleaned from time to time.

Switch your pH meter or controller off
Detach the electrode from the meter or controller carefully
Rinse the electrode under tepid water for about 2 minutes, holding only the sensing tip under the stream of water, not the entire electrode
Use a very very soft brush to remove visible dirt. I actually use a kitchen sponge type brush. That seems to work very well for me. It takes a little longer but no damage to the electrode will occur
Rinse the electrode again under tap water for a minute or so
Visually inspect the tip for remaining dirt, then go to the next step
Use your soft brush again
Place the electrode tip in a very mild acidic solution for about 2 minutes. A 3 percent muriatic acid solution is fine to do so.
Rinse under tapwater for a minute
If you can, now rinse the electrode for a few minutes under treated water. This can be reverse osmosis, deionized, distilled or otherwise treated water

This treatment should have cleaned your electrode pretty well and all dirt, detritus, compounds that settled on the tip, etc. should have been removed. Even materials or compounds that encrusted the electrode should be gone as well.

Calibration of the pH Electrode

The electrode is now clean and we can now proceed to the calibrating stage which is the key to getting an accurate reading. Use very good quality standards to do so. Do not make up your own or let the calibrating standards sit around for too long as th ey will be "off" and you will not be calibrating accurately.

The calibrating procedure should always be done with at least two pH reference standards. This can be a pH 4 and a pH 7, or a pH 7 and a pH 9 or a pH 10, or any combination of these standards. I use 4 and 7 myself but there is no need for you to do so. You can use any combination of the pH standards mentioned earlier.

Follow the directions given by the manufacturer closely. They vary at times. Not all meters/probes will be identical in their instructions.

Below though is an example of how an Octopus Controller pH electrode gets calibrated. This should serve only as a guideline as the procedure for your particular meter or controller may not be the same. Also, pen-type meters and full size meters may hav e different procedure and may require turning little screws or knobs, as opposed to the Octopus unit which self-calibrates (which is a big advantage of course).

Never touch the standard solutions used to calibrate with your fingers, or hands, and do make really sure that the container you use to place them in is dry and clean.

Rinse the electrode in treated water
Set controller in the calibrating mode
Place the electrode in pH 7 solution and wait
When the auto calibration is finished for pH 7, rinse the electrode in treated water
The Octopus display will now ask you to place the electrode in a pH 4 standard solution
The meter auto-calibrates
When this procedure is finished, rinse the electrode in treated water and place it back in your tank or sump
Set the meter again for "measuring" the pH rather than for calibrating the electrode

Most meters/controllers will not make it that simple for you. You will need to manually adjust the meter to read the value of the pH standard solution you are using because there are not many auto-calibrating units on the market.

Calibrating is not complicated though. Just follow the directions that came with your unit.

Some hobbyists will calibrate their meter and electrode and when that is finished will do so again a second time hoping to get a greater accuracy in that manner. There is nothing wrong in doing so. What you must do though is use new pH standards when y ou perform a dual calibration. Do not reuse the ones you used the first time because they are contaminated. You need to use new ones.

Should you have any questions regarding calibration and cleaning you can leave us a message by clicking on our Internet address below:

tat@3pco.net