pH Probe Problems?
Help! My pH readings are wrong!
One of the most frequent phone calls I receive is a Bayrol dosing controller displaying pH readings that differ from a poolside test. There are many factors which can cause this and here we will look at some of the most common.
How clean is your equipment?
The cleanliness of the sample line and measuring cells can have a significant impact on pH readings. As the years roll by on an installation measuring cells can become contaminated and clog up. Injectors can be particularly vulnerable to this and can be easily blocked.
Clean Sample Chamber
Dirty Sample Chamber
Here you can see a new cell compared to one which requires cleaning. This contamination can affect the pH and Cl readings and can cause back pressure which will affect the dosing pumps. Make sure your measuring cell and filter are kept clean especially when fitting new probes or electrodes.
Does your probe have salt rings?
When pH probes are shipped they have 3 white rings of salt around the glass tube. These rings dissolve as the probe ages and are a great indicator of the life left in the probe. Now I’m sure you all read the information leaflet contained in the box that the probe came in but it does actually contain some useful information.
Keeping probes clean and not letting them dry out are 2 ways of maintaining the life of the probe and storing them upright as long as possible is definitely a benefit. When your probe no longer has salt rings it’s definitely time to change it. Under normal operation, your probe should last 12 months so include a new one as part of an annual service.
Have you Calibrated?
An essential part of the measurement process is calibration of the pH probes. If our measurement cell is clean and the probe has plenty of life left in it calibration should be a straight forward process. Bayrol recommend calibrating at first commissioning or recommissioning, water change, new electrodes and at regular intervals - at least once a month. Follow the calibration instructions in the manual supplied with your dosing controller and make sure you have some new pH7 buffer solution to hand. If the pool has been shock treated or has had a water change, make sure the sample lines have been flushed through to ensure that any old water has been flushed out of the measurement cell.
So, it’s clean, it’s a new or good probe and it won’t calibrate. What next?
Something that’s often missed when installing Bayrol controllers is the ground connections. Where ground connections are required, the necessary cable is included in the installation pack shipped inside the controller packaging. These ground connections are in addition to the earth connection in the 230v mains connection and should be installed in accordance with the installation instructions. Essentially one end of the cable attaches to the metal tag on the sample line saddle clamp whilst the other end should be connected the same connection as the earth cable in the 230v supply to the controller. This connection ensures that the potential earth (ground) of the pool water (the tag on the sample line connection) is the same as the earth potential of the controller. If there are potential differences in the pool water and controller and this connection isn’t made then the controller may not be able to read the probe measurements correctly. If the manual says fit one, fit one!
And finally…
If you have done everything suggested and your poolside pH test still deviates significantly from the Bayrol controller then give us a call here a Lighthouse Pools.
Post by Jim Powell - Lighthouse Technical Support