pH and ORP readings way off all of a sudden

[pclausen]

Yesterday morning my pH and ORP readings went completely berserk. Here is a plot of the reading over the last 24 hours. Any idea what is going on? I'm going to go pick up a regular pH test kit, but I hardly believe that my pH is around 3 right now! Notice how the ORP and pH are exact mirror images of each other? Something odd must be going on. Readings have been reasonable for week prior to yesterday. I wonder what the heck went wrong?

 

[pclausen]

Let me add that my ORP and pH probes are about 10" apart and that I am using the serial isolator. I tried disconnecting the serial cable, but that didn't change the readings at all. I also cleaned both probes to no avail.

When I lift the probes out of the water, pH goes from ~3.5 to ~7.5 and ORP drops from 620 down to around 400.

As you can see from the graph, pH and ORP values continue to appear to be mirror images of each other.

 

[Acroholic]

Hey PC, I was just reading your thread and I noticed you said that you had cleaned your pH & ORP probes, but have you checked your TEMP probe? From what I understand, the Temp probe is the ground reference for the pH & ORP probes. Make sure you should clean it and re-calibrate it and make sure it is re-installed within the 6" limit?
Good luck....

 

[pclausen]

I also checked the temp probe. According to the instructions, you are supposed to leave the plastic cap on the temp probe, so I have been doing that. I just cleaned the outside of the plastic cap. Didn't make a bit of difference. I also unplugged the temp probe and the pH and ORP did begin to fluctuate.

All 3 probes are mounted in the piece of floating Styrofoam that is about 12" long. pH and ORP probes are about 10" apart with the temp probe in the middle.

All readings were normal until Saturday morning around 9 am, when the pH and ORP probes lost it. Both are the lab grade probes and have only been in use for a month.

 

[pclausen]

I'm going to order some more 7.0 and 10.0 fluid packs today and recalibrate the pH probe, but I'm not sure that is going to correct the problem being that the ORP probe is also whacked.

 

[dougc]

I have seen wacky readings caused by electrical currents in the water from a malfunctioning heater. Is all of your equipment on GFCi? I would try filling a container with some tank water and floating the probes in that to rule out such interference.

Since both ORP and pH are way off, it is unlikely that the problem lies with either of those, but I guess that it could be a problem with the temperature probe.

I'm sure that Curt will weigh in later with some ideas, but it is still very early on the Left Coast.

 

[pclausen]

Good idea about floating the probes in another container. Just so happens that I have a 44g BRUTE sitting next to the sump with fresh sw in it. I'll disconnect the submerged Mag 9.5 mixing pump from it and float the probes in there to see what happens.

My system is running off two dedicated 20A GFI circuits. The sump that the probes are floating in also contains 2 250W Ebo-Jager heaters and an ASM G6 skimmer with its 3 submerged Sedra 9000 pumps. The skimmer is only a month old, the heaters a little over a year. But the heaters aren't typically running this time of year.

At any rate, let me float the probes in another body of water to rule out some sort of current leak.

 

[clp]

Here are some things to try:

- unplug the probes one at time and see if it effects the other probes readings.
- unplug the serial cable and see if it effects the readings
- place each probe one a time in a cup of your tank water and see if its reading changes.

Let me know what you find.

Curt

 

[pclausen]

- unplug the probes one at time and see if it effects the other probes readings.

No change in the other probes readings

- unplug the serial cable and see if it effects the readings

No change

- place each probe one a time in a cup of your tank water and see if its reading changes.

When I moved my entire Styrofoam tray to another container (4 day old mixed sw), readings returned to normal (pH 8.04, ORP 360).

I then put the tray back in the sump and for a few minutes the readings were correct, then they went bad again. I re-arranged the wires a bit (uncoiled the pH and ORP wires), and the readings again went back to what appears to be close to normal.

Looking at the graph for the last 24 hours however, I'm still not sure I'm out of the woods.

 

[clp]

If the probes give the same reading when in a cup of tank water, then they most likely reading correctly. The pH and ORP values graphed look reasonable especially if you are running a Ca reactor and/or have low alkalinity.
I'm wondering if there is cut in one of the probe wires which is causing the readings to go out of wack when it shorts with the tank water.

Curt

 

[pclausen]

Thanks Curt. I think I'm going to unplug the ORP probe for a bit and clean and re-calibrate the pH probe and run it like that for a while. My Ca reactor isn't online yet but I know my alkalinity is low right now. I should have my kalk reactor up and running in a couple of days to bring the pH, Ca and alk back up.

I don't plan on bringing the Ca reactor online until I have enough corals in the tank to warrant it as the kalk reactor should be able to handle my needs until then I would think.

 

[docjay]

The pH and ORP graphs still look like mirror images to me. That's got to be some artifact. What are the chances that two unrelated parameters would be mirror images when graphed?
I also noticed this same thing in the screen shots for aquanotes on the neptune systems website.
So what's up with that?

Jay

 

[clp]

There is a inverse correlation between ORP and pH. For every 1 unit of pH change the ORP changes by about 58 mV. The graph looks very typical.

Curt

 

[docjay]

Curt, I'm not arguing with you, you are the expert for sure. I'm just trying to understand this. If this inverse relationship exists why do we need an ORP meter? Why not just have aquanotes do the calculation and give us ORP from pH. ORP can drop significantly with even a heavy tank feeding. Why don't we see significant pH swings with feeding?

Thanks,
Jay

 

[Member No. 1]

Curt, I'm not arguing with you, you are the expert for sure. I'm just trying to understand this. If this inverse relationship exists why do we need an ORP meter? Why not just have aquanotes do the calculation and give us ORP from pH. ORP can drop significantly with even a heavy tank feeding. Why don't we see significant pH swings with feeding?

Thanks,
Jay

Like I would know... but here goes...
You don't see a big swing in pH due the the heavy buffering capabillities of the water. There is nothing to buffer an ORP loss.
You can't get a ORP reading in a direct relationship with pH. Example:
ORP start... 200mV ph goes down 1 unit ORP goes up 58 mV 258mV now.
ORP start ...300mV ph goes down 1 unit ORP still goes up 58 mV.

So if pH is at a certian level, how would you tell what your ORP is?
You can tell what it will change, but you have no base from which to start from.

See... I told you I didn't know.

 

[clp]

Member No. 1 is right, you won't know the base ORP just by looking at the pH value. Correlation between different parameters is quite common. For example:

pH is correlated w/ temperature (weak correlation).
Cond. is corralted w/ temperature (med. correlation).
DO is correlated w/ salinity, temperature, and altitude.
ORP is correlated w/ pH.

Curt

 

[docjay]

So the fact the the Graphs are mirror images is really a function of the scaling of the y-axis?

 

[clp]

Yes, I believe so. ORP is remaining constant or nearly constant.

Curt

 

[pclausen]

I continue to have issues w/ my probes. It seems that anytime I move the Styrofoam float or the wires, the reading gets skewed. Seems like a loose connection with one of the probes. Temp is stable, but both pH and ORP drift (pH goes down and ORP goes up). Disconnecting any one probe doesn't change the readings of the others. Any suggestions as to how to proceed?

 

[clp]

It sure seems like a ground loop. Leave the serial cable unplugged for 24 hours, and then look at the datalog. Perhaps the serial isolator is not isolating.

Curt