Are the cheap pH pens on TM any good

[Asmodeus]

Or are they junk? Any feedback or accuracy reports? cheers

[amtiskaw]

Do you mean the yellow ones with the black cap? I've got one of those and it's accurate. They've gotten cheaper, I paid ~$60 for mine a while back

[Asmodeus]

Yeah, they're like $25 now

http://www.trademe.co.nz/pets-animals/f ... 115967.htm

Good to know they work

[Asmodeus]

Or $16 if you look outside the pets section

http://www.trademe.co.nz/business-farmi ... 779880.htm

[Jennifer]

These probes are only as good as three things:

1. the quality of the probe tip

2. your care of the probe tip

3. the calibration range you set it to

With regard to the quality, you get what you pay for. I paid for a tip that cost $100 - just for the tip alone, but that was for a sensor that would dose CO2 and I didn't want it to be wrong and gas all of my fish.

With regard to the care of the probe, most of these need to stay wet or they will degrade very quickly (like overnight) rendering them useless. usually they are meant to sit in a neutral (pH 7.0) buffer when not in use. Find out what the manufacturer recommends and stick to it closely for best performance and lifespan.

With regard to the calibration, most of the electronics that make up the pH probes have a pivot point at pH 7.0, like a fulcrum. The pivot point is fixed at 7.0 with the slopes going either side. What this means is that you need to calibrate it to high OR low pH, but not both. To calibrate it, you need a set of pH buffers. For example, if you were going to calibrate at low pH so that you could detect fluctuations around 6-6.5, you would want to put the tip in a buffer around pH 5 and set the probe so that it is correctly reading 5.0 when it is in that buffer. Then, rinse it off and put it in the pH 7 to verify it is correctly reading 7.0. Always rinse and tap dry between buffers or you will contaminate them. Calibration should take place often, every use even and it is important to remember that if you try to read a high pH with a low calibrated probe, it may not be accurate.