Randy Holmes-Farley
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My Tank Thread
When I took down my tank 8 years ago, I got rid of nearly everything. One thing that remained in the fish room cupboard is a ceramic mug containing a bunch of pH probes, some of which are pretty high end. For example, two are Ross pH electrodes. Fisher Scientific currently is selling them for $722 each (I didn't originally buy them, but got them used from places I worked for that no longer needed them).
Once upon a time they were in some type of water in the mug. I don't recall what it was. Maybe tank water, but probably tap water.
A couple of weeks ago, I went to figure out if anything was salvageable. I tried to pick up the mug by the handle and the mug literally broke into a dozen pieces. Of all the things I thought I might find, that was not among them. It was from a family reunion long ago. They probably bought the cheapest mugs available. lol
Of course, there was no water left, just dried salts. Even inside the probes they looked entirely dried out.
The glass bulb of a typical pH probe is a very important piece of hydrated thin glass that allows measurement of pH. The way it does that is surprisingly complicated, and I discuss it here for anyone interested in more details:
reefs.com
This little section from it summarizes the effect:
The glass used in a pH electrode has a composition that includes certain metals in addition to the usual silicon and oxygen of SiO2 glass. These metals can include lithium, barium, lanthanum, sodium, and calcium, among others. At both the inside and outside surfaces of the glass bulb (and also in a thin (50 nm) swollen region of hydrated glass on each side), there is some substitution of H+ for these cations. How much substitution depends on how much H+ is in solution, and hence on pH. The internal pH does not change, but the external pH does, so the amount of substitution on the outer surface changes while on the inside it does not, setting up a potential difference across the glass membrane that depends on pH.
Note in that description is the mention of a hydrated layer on the glass. That is why one does not want them to dry out. A pH electrode that has been sitting dry for years has certainly changed the nature of the hydrated glass, and it may well never be recoverable.
But why not try?
So this is a long term experiment to see if I can get any of these probes suitably working again.
First step was to refill the insides of them. All (IIRC) were refillable through a hole in the body. Some pH electrodes are sealed, but not these. I only had one filling solution available (also sitting on the fish room shelf). Some different pH electrodes use different filling solutions, but I'm not sure what happens if they are not exactly matched. Most are a fairly concentrated potassium chloride solution, and some are saturated with silver chloride as well. I think it was a Ross filling solution I used, but I'll have to double check that.
After filling them all, the next step was to try to rehydrate them on the outside. I'm not sure if that will work or how long it might take. I placed them all into a container of tap water and started them off soaking.
In the near future, I'll be seeing if I can get an old pH meter working again (found a meter behind a box in the old fish room but so far, not the cord lol) and then see if these are at all responsive to pH.
Assuming they do respond to pH, then I'll see if they can be used with actual calibration fluids to give useful values.
So no answers yet, just a long slow work in progress.
Happy reefing. :)
Orion™ ROSS Ultra™ Glass Bodied Combination pH Electrode BNC (Waterproof) | Buy Online
Orion™ ROSS Ultra™ Glass Bodied Combination pH Electrode. Conduct precise pH determinations with this general purpose, top performance glass body combination electrode with waterproof BNC connector. Available in BNC (Waterproof)
www.thermofisher.com
Once upon a time they were in some type of water in the mug. I don't recall what it was. Maybe tank water, but probably tap water.
A couple of weeks ago, I went to figure out if anything was salvageable. I tried to pick up the mug by the handle and the mug literally broke into a dozen pieces. Of all the things I thought I might find, that was not among them. It was from a family reunion long ago. They probably bought the cheapest mugs available. lol
Of course, there was no water left, just dried salts. Even inside the probes they looked entirely dried out.
The glass bulb of a typical pH probe is a very important piece of hydrated thin glass that allows measurement of pH. The way it does that is surprisingly complicated, and I discuss it here for anyone interested in more details:
Aquarium Chemistry: Measuring pH with a Meter
This article describes how pH meters work, how to select one to use, and how to best use it to measure the pH of a reef aquarium.
reefs.com
This little section from it summarizes the effect:
The glass used in a pH electrode has a composition that includes certain metals in addition to the usual silicon and oxygen of SiO2 glass. These metals can include lithium, barium, lanthanum, sodium, and calcium, among others. At both the inside and outside surfaces of the glass bulb (and also in a thin (50 nm) swollen region of hydrated glass on each side), there is some substitution of H+ for these cations. How much substitution depends on how much H+ is in solution, and hence on pH. The internal pH does not change, but the external pH does, so the amount of substitution on the outer surface changes while on the inside it does not, setting up a potential difference across the glass membrane that depends on pH.
Note in that description is the mention of a hydrated layer on the glass. That is why one does not want them to dry out. A pH electrode that has been sitting dry for years has certainly changed the nature of the hydrated glass, and it may well never be recoverable.
But why not try?
So this is a long term experiment to see if I can get any of these probes suitably working again.
First step was to refill the insides of them. All (IIRC) were refillable through a hole in the body. Some pH electrodes are sealed, but not these. I only had one filling solution available (also sitting on the fish room shelf). Some different pH electrodes use different filling solutions, but I'm not sure what happens if they are not exactly matched. Most are a fairly concentrated potassium chloride solution, and some are saturated with silver chloride as well. I think it was a Ross filling solution I used, but I'll have to double check that.
After filling them all, the next step was to try to rehydrate them on the outside. I'm not sure if that will work or how long it might take. I placed them all into a container of tap water and started them off soaking.
In the near future, I'll be seeing if I can get an old pH meter working again (found a meter behind a box in the old fish room but so far, not the cord lol) and then see if these are at all responsive to pH.
Assuming they do respond to pH, then I'll see if they can be used with actual calibration fluids to give useful values.
So no answers yet, just a long slow work in progress.
Happy reefing. :)
