Intresting pH readings

[woodnaquanut]

I have two pH probes in my tank. First one came with the used Apex and since I have no history with it, I decided to add one as a comparison. The second one has always been about 0.1 higher than the original one. I noticed today the values have swapped places. Now the newer one is reading lower than the original.

Cleaning and recalibration is on my 'to do' list today!

Since everybody likes pics:

<a href="http://s1160.photobucket.com/user/aqua-nut/media/random%20pics/pHchart.png.html" target="_blank"><img src="http://i1160.photobucket.com/albums/q484/aqua-nut/random%20pics/pHchart.png" border="0" alt=" photo pHchart.png"/></a>

 

[woodnaquanut]

A couple of more pics. I'm still mystified why they don't read the same pH.

First, right after calibration:<a href="http://s1160.photobucket.com/user/aqua-nut/media/random%20pics/Screenshot2014-01-29at42742PM.png.html" target="_blank"><img src="http://i1160.photobucket.com/albums/q484/aqua-nut/random%20pics/Screenshot2014-01-29at42742PM.png" border="0" alt="ph right after calibration photo Screenshot2014-01-29at42742PM.png"/></a>


And after a few hours:
<a href="http://s1160.photobucket.com/user/aqua-nut/media/random%20pics/1bb042f9-6e23-4d13-a821-e155bb9925c2.png.html" target="_blank"><img src="http://i1160.photobucket.com/albums/q484/aqua-nut/random%20pics/1bb042f9-6e23-4d13-a821-e155bb9925c2.png" border="0" alt=" photo 1bb042f9-6e23-4d13-a821-e155bb9925c2.png"/></a>

 

[Dragonvale]

Where is each probe located? That's weird.

 

[woodnaquanut]

They are in the same probe holder.

 

[zeroinverse]

Sometimes you get salt creep and stuff in the BNC connectors.. That can impact the readings.

The other things could be you programmed the channels and accidentally swapped them mid way?

 

[woodnaquanut]

I think you mistake my post. I expected the switch in the last picture. The probes have been drifting, in opposite directions, for the last few days. Since I installed pH2 it has read higher than the other. Now, after calibration, it again reads higher than the first pH probe.

The first probe is older. I don't know how much older, it came as part of the used Apex I purchased.

The big mystery to me is why they are not reading the same. If I only had one probe this would not be an issue!

 

[Dragonvale]

That calibration solution has a set point right? Like 8.0? I think your suppose to use two sets if I'm correct. Anyways, can't you just test each probe by dipping it in a 8.0 solution and see which ones off?

 

[woodnaquanut]

That calibration solution has a set point right? Like 8.0? I think your suppose to use two sets if I'm correct. Anyways, can't you just test each probe by dipping it in a 8.0 solution and see which ones off?

That's the funny part. After calibration both probes have the correct readings for the pH 7.0 solution. I'm not that worried about the differences. I'm more interested in the trend. I've also had the 'feeling' the old probe always reads low.

 

[crispyreef]

You could be losing the response on one of them due to being old.

 

[woodnaquanut]

You could be losing the response on one of them due to being old.

I think I do have a problem. The 'new' probe seems to be sliding way off calibration. Here is the last seven days of readings.

<a href="http://s1160.photobucket.com/user/aqua-nut/media/random%20pics/Screenshot2014-02-06at104829AM.png.html" target="_blank"><img src="http://i1160.photobucket.com/albums/q484/aqua-nut/random%20pics/Screenshot2014-02-06at104829AM.png" border="0" alt="7 day record photo Screenshot2014-02-06at104829AM.png"/></a>

 

[Dragonvale]

I think I do have a problem. The 'new' probe seems to be sliding way off calibration. Here is the last seven days of readings.

<a href="http://s1160.photobucket.com/user/aqua-nut/media/random%20pics/Screenshot2014-02-06at104829AM.png.html" target="_blank"><img src="http://i1160.photobucket.com/albums/q484/aqua-nut/random%20pics/Screenshot2014-02-06at104829AM.png" border="0" alt="7 day record photo Screenshot2014-02-06at104829AM.png"/></a>

So what does it mean? A new unit needed? To me calibration then a new probe and your still getting mixed readings? Contact apex if they have a sponsor thread on rc and just post this thread. I'm sure they will have a solution. Weird.

 

[bogdanek]

If these are the cheap probes Made in China for 20$ their reading accuracy is probably +/- 0.25. So it shouldn't be a surprise that they read differently. When using the pH meter with the controller one should be aware that the reading is not accurate. It is just the trend that we can follow and see a significant sudden changes. Think about it as an alarm device rather than measuring device.