Ph Pen, is it working properly ?

[dao]

So I have simple one-point calibration PH Pen, which are all over Amazon and I am not sure if it works properly.
I store in KCL buffer, and calibrate to 7.0 buffer. I rinse in RO water between uses.
Now the pen recognizes the pH of the buffer really quickly, although after a short time of storage like 1-2 days it is usually off by 0.1
In my tanks however the readings take much longer to stabilise, and what puzzles me the most is the fact that the reading is lower when I place the pen in a strong water current, and higher when I place it in a still water. Should it work that way? If yes I assume the reading should be taken in still water only ? Are these single point calibration pens decent for the price, or are they a waste of money ?

[ibebian]

I *think* that electrical interference from hardware like powerheads can affect the reading. Curious about this too, so would be great if someone more knowledgeable chimed in!

[Brolly33]

Stray tank voltage can throw off pH probes a lot.  Suggest taking the water out of the tank in a glass to test it.

[Mr. F]

So I have simple one-point calibration PH Pen, which are all over Amazon and I am not sure if it works properly.

I store in KCL buffer, and calibrate to 7.0 buffer. I rinse in RO water between uses.

Now the pen recognizes the pH of the buffer really quickly, although after a short time of storage like 1-2 days it is usually off by 0.1

In my tanks however the readings take much longer to stabilise, and what puzzles me the most is the fact that the reading is lower when I place the pen in a strong water current, and higher when I place it in a still water. Should it work that way? If yes I assume the reading should be taken in still water only ? Are these single point calibration pens decent for the price, or are they a waste of money ?

The pH sensor works by constantly binding H+ ions to its surface. If the water is moving, there is a higher incidence of H+ per unit time, so you should see a lower reading than in still water. However, due to the logarithmic nature of pH, it shouldn't be very drastic.

[Vpier]

21 hours ago, dao said:

So I have simple one-point calibration PH Pen, which are all over Amazon and I am not sure if it works properly.
I store in KCL buffer, and calibrate to 7.0 buffer. I rinse in RO water between uses.
Now the pen recognizes the pH of the buffer really quickly, although after a short time of storage like 1-2 days it is usually off by 0.1
In my tanks however the readings take much longer to stabilise, and what puzzles me the most is the fact that the reading is lower when I place the pen in a strong water current, and higher when I place it in a still water. Should it work that way? If yes I assume the reading should be taken in still water only ? Are these single point calibration pens decent for the price, or are they a waste of money ?

The cheaper pens are not very good or reliable. They have to be cleaned, stored correctly and re-calibrated often. The pens will read a small volume of water like when your testing much faster than a larger one like a tank. Moving water will affect the reading. Also there are many many factors in your tank that will cause PH to change from day to day, week to week and month to month. Water changes, water temps, evaporation, leaves/botanical's, plants, CO2, wood, decomposition, substrate and even what time of the day it is. PH is never a stable thing.  I have well water and my well is 68ft underground. My well water's PH will change during certain times of the year.

If your cheaper pen is off by 0.1 then I wouldnt be worried, thats really good because I had a pen that would give me several different reading in the same tank and would be off by 3.0.