pH probe with transparent gel formation on sensor.

[A. Grandis]

Hello all,

I've got a Milwaukee pH/ORP controller for my zoa tank and the pH meter shows aways much lower numbers than the water actually is.
I have to clean the sensor every day to be able to see the real pH value, due to a transparent gel that forms on the bubble glass sensor.
Here is a picture:

Does anyone here knows why that gel forms and what exactly IS the gel?
I think it could be formed by bacteria, but why only on the probe? Perhaps the sensor would have electrons exchanged or something like that?
Any tips on how to prevent the gel?

Aloha,
Grandis.

[bertoni]

I'd guess you're seeing bacterial growth. I don't know how to discourage the growth, though. Maybe moving the probe away from light (as appropriate) or to a place with a different flow rate might help.

[A. Grandis]

Hummm... No light nor flow where probe is (sump).

Grandis.

[Randy Holmes-Farley]

Bacteria seems a good guess, but the probe might also be leaking somehow and causing a precipitate when it hits the seawater. Many are gel filled, and the silver inside will preciptiate silver chloride, although I wouldn't expect that to be clear.

Are you dosing organic carbon?

[wolfblue]

I'm more with Randy on this one. The bio deposits I see on probe tips looks more like a fatty substance and it takes a week or more to start to show any at all.

[woodnaquanut]

I had two pH probes. Right next to each other. One has the goo the other doesn't. The goo one always reads low by about 0.3.

I'm of the opinion it's leaking.

[A. Grandis]

Thanks for the replies!!

I'm not dosing organic carbon. I actually export organics using GAC and doing partial water changes every week.
The system doesn't have the gel anywhere but on that probe. The ORP probe doesn't have the gel either.
I had a Pinpoint pH monitor before and that also had the same gel structure. That's why I was thinking of bacteria. The Pinpoint monitor stopped working and I've got the Milwaukee. I've got the Milwaukee for more than a year working great, except for the gel, as the Pinpoint.

The gel has aways been there. The system is more than 6 years old, so I don't think it is any type of leak from the probe. Unless the leak is very very tiny and the gel is, like Randy said, a precipitation. And then all the probes would have to have the leaking problem (?).

The pH reads really low, sometimes down to 7.5. When I clean it goes back to the 8.0 - 8.4, depending on the time of the day.

I calibrate the probe every 2 months or so.

If bacteria, I would like to understand chemically why does the gel forms?

Cheers,
Grandis.

[disc1]

Bacteria often form biofilm that look like gel. It is a bunch of bacteria all growing together and sticking to each other.

[A. Grandis]

The probe must attract that specific species of bacteria, I would presume.
I would like to understand why?
I mean, what attracts the bacteria to the glass bubble (sensor)?
Any thoughts Randy?

The picture shows like a drop, but it actually covers the whole glass when in the water. It drips when removed from the water.

Grandis.

[A. Grandis]

Please take a look at this nice video:

The silver, silver chloride is actually the wire on both compartments. The solution is actually potassium chloride on both compartments.

I think the bacteria begins to build up, as on any other surface in the system, and the environment around the probe somehow allows them to grow better due to the ion exchange. With the barrier made by the bacteria gel formation, there is a higher concentration of hydrogen ions to the glass bulb (sensor), therefore showing the lower pH on monitor. There is also a possibility of the potassium chloride from inside of the tube to somehow help the process because the junction doesn't totally disconnect the electrical connection between them.

The outer glass of the bulb is actually called the " gel layer". Hummm...

Please feel free to discuss..

Grandis.

[Randy Holmes-Farley]

I'm not sure why bacteria would grow there over and over after removal.

The outer glass of the bulb is actually called the " gel layer". Hummm...

That's not the sort of gel you are seeing or I was referring to. That is just hydrated glass.

The gel I was referring to is inside of gel filled electrodes, which then are not just KCl but have a gelling material (usually an organic polymer of some sort) inside and generally are not refillable.

FWIW, silver is released from the wire inside the electrode as it operates and sometimes precipitates as silver chloride inside. I think it is unlikely to be silver chloride outside since it is clear, but if the electrode is leaking, a small amount of silver can be released.

[A. Grandis]

Thanks very much, Randy!!

I just thought was interesting to see the term "gel" on the movie. I knew that wouldn't have anything to do with the formation over the glass. LOL!!

I'll try to collect a sample and look under the microscope. Perhaps the gel is indeed pure bacterial film as I was thinking since the beginning, but hard to fully understand how that works. I still think that, if indeed bacterial film, it would be a specific species of bacteria. The transparency of the film is unique.

Very interesting...
Please let me know if there is anything you would think I could do to prevent the formation of the gel.

Grandis.

[Randy Holmes-Farley]

It is the dreaded glass eating bacteria, close cousin to the flesh eating bacteria you hear about on the news. You just don't make the 6 pm news by having a pH probe eaten.

[A. Grandis]

LOL!!! I think the bacteria actually gets high on the glass/ions instead eating it. LOL!!!

The gel in the microscope:



Grandis.

[loudell]

the inside gel is leaking; most likely a failed construction issue...

[A. Grandis]

Alright... I'm pretty busy nowadays and finally got a time off to check on the probe.
pH was 7.1 and the gel was really thick this time.
Please take a look at the pictures below:
pH probe with the gel out of the water, close to the surface.

The gel:

Please notice that after more than a week letting the gel alone it shows some white coloration.

Now... I looked the gel on my microscope and many types of creatures were attached to the structure. Most would probably be bacteria of a light color, kinda greenish, very tiny.

I've got more probes in the tank and only that particular one shows excessive growth of the gel. The ORP also has a bit, but almost unnoticeable.
I've got another pH probe for the ReefKeeper and the temperature probe for the same, no build ups.

Any more thoughts?

My goal now is to know if anyone here would be familiar with what the gel would look like in the microscope, if it would be bacterial build up.
Would that be full of bacteria only, with no spaces?
Spaces between the pockets of bacteria?
Colors?
Could other microscopic organisms be attached to it?
Thanks,

Grandis.

[bertoni]

I think you'd need a microscope and some skills in bacteriology to get an idea of what's happening.

[Randy Holmes-Farley]

Further, bacteria will coat just about anything int eh tank, even if that wasn't its origin.

FWIW, I've never seen or heard of this happening.

The gel is nowhere else in the system that you can see?

[ca1ore]

FWIW, I have this exact same yellow probe and mine grows a similar goop, though not as fast and it's a pink color. None of my other probes are so affected, although this was the only one in the dark. Since I moved it to a lighted spot no goop.

[A. Grandis]

Originally Posted by bertoni

I think you'd need a microscope and some skills in bacteriology to get an idea of what's happening.

I've got the microscope, but not the bacteriology skills...

Grandis.

[A. Grandis]

Originally Posted by Randy Holmes-Farley

Further, bacteria will coat just about anything int eh tank, even if that wasn't its origin.

FWIW, I've never seen or heard of this happening.

The gel is nowhere else in the system that you can see?

I though I've seen some on the ORP probe, but took a closer look and there is nothing there.
I had similar gel formation in the past on another Pinpoint pH probe, but not as thick.

Tank is 6+ year old. No, the gel nowhere else in the system, as far as I can see.
I've got many types of inverts on my artificial rocks introduced with natural water through the years, like sponges, snails, hydroids, worms, etc...
Sand is thin, oolitic sugar size aragonite, about an inch to inch 1/2 high. No signs of bacterial films on/in the sand at all. System is well fed and clean, algae free, with healthy organisms.

I'm still trying to connect the chemistry around the glass bulb attracting that specific bacteria and allowing a perfect environment for it.
Indeed very interesting.

I've contacted Milwaukee about that to see what they think, but they didn't reply yet.
I was thinking to purchase the new pH monitor from Milwaukee and see what happens.

I'll keep you posted.

Grandis.

[A. Grandis]

Originally Posted by ca1ore

FWIW, I have this exact same yellow probe and mine grows a similar goop, though not as fast and it's a pink color. None of my other probes are so affected, although this was the only one in the dark. Since I moved it to a lighted spot no goop.

That's very interesting! My probe is in the sump, and it's dark also. Not completely dark though.
Hummm...
Pics please?

Grandis.

[ca1ore]

No goop to take a picture of, sorry. The other thing I did was to install this probe into the recirculation stream of my calcium reactor and the strong flow around the tip also helps to keep it clean.

[A. Grandis]

Thanks ca1ore!
I'll see what I can try here.

Please keep your ideas coming...

Grandis.

[A. Grandis]

Ok, I still didn't change the probe around...

The answer from Milwaukee was that " Seal has gone out...".
Therefore I'm assuming the gel indeed comes from inside of the probe and the bacteria seen in the gel is evidently just taking advantage of the substance to grow in/on it.
They suggested to get a new probe (MA911B/2).

Grandis.