Cloudy PH Probe

[thekameleon]

So I think my PH probe is bad. beyond my readings the fluid inside is now cloudy. For those of you that understand how the PH probe works, and suggestions on preventing this in the future or why it would become cloudy in the first place?

[brimarq]

I had a problem with several pH probes all in a row. Look at the "O" ring that seals the glass bulb to the acrylic housing. Does it look like it may have worked it's way down to were the serrations in the housing let water flow over bulb? Once the "O" ring gets to the serration saltwater gets inside the housing and the fluid inside gets cloudy, my pH reading went down to 3 or 4 every time as well. I have yet to get an answer from anyone but I'm convinced the cause was stray voltage from a Mag 14 return pump. I figured out I had a stray voltage issue first, put my voltmeter ends in water and got a reading, then started unplugging stuff till I determined the cause. I'm not sure exactly how the stray voltage messes with the probe but I have not had any issues since I figured this out. Best I can determine is there is a pressure build up inside which pushes the "O" ring out. My corals all took off significantly as well since I replaced return pump. Not sure this is your problem, but I definitely think your Ph probe fluid may have gotten contaminated with salt water.

[thekameleon]

I have suspected stray voltage as well, but I have been unable to pin it down. I have unplugged every single device form my tank and it still shows a potential between ground and the tank. After a little research, I found that the magnets in the motors them selves can actually show voltage and it is not so much the voltage you have to worry about but actual current. Voltage just measures the potential, current is the actual flow. I have tried unplugging all of my devices and re-plugging them in one at time, but the results are inconclusive.

To resolve this I am building a new assembly for my probes that isolates each probe I have in its own small tube that holds just enough water to keep the probe submerged (half a cup or so). I will then use a small lift pump to lift water into the tubes and have the water drip into the tubes, then each tube would have n overflow that drips back into the sump. The idea is to isolate the probe from the tank, yet get a current reading.

As for the stray voltage, I do measure about 0.12 volts in the tank.... So I doubt it would be the pumps as it would be much higher if it were especially since I tried measuring the voltage right at the pump, powerhead and heater housings housings with no difference. I also measure about the same voltage when everything is turned off and measure zero current between ground and the tank with the grounding probe removed. So I think I am covered... I'd pay money for someone to build a stray voltage alarm/sensor... Roberto? LOL

[enigma32]

Unless you're using a fairly decent multimeter 0.12V could just be junk data. What measurement range are you using when it reads that?
It also could be that the potential of the tank is "floating" if you disconnected all power (by literally pulling all of the plugs, not just switching them off) and were still reading this with the ground probe removed, but saw this change to 0v when you placed the probe in the tank again.
Another possible reason is that, if you left some things physically plugged in to an outlet, you may have a potential difference between neutral and ground in your household wiring and it is carrying across into your tank somehow. A small difference like this is not uncommon.

I like your idea for isolating the probes... it's a pretty ingenious solution to help narrow down the problem with the probe itself. I'll be curious to see if that fixes the problem of the dying probes

[thekameleon]

I physically pulled the plugs and removed the ground probe. I was using the 200 mV range which was consistent with the 2V range as well.

As for the probe isolation, I have a tap plastics place close by so I just need to spec it out. I have to believe that the multiple probes in the water also have to effect each other since they all do measure some type of current/voltage difference. Once I figure out a design that works and try it out, I will definitely share the specs.

[dapg8gt]

Im building a manifold for my probes out of pvc and 1\2" john guest fittings that the probes fit into perfect no leaks. But im guessing since its gonna be supplied by a submersible it will carry over the voltage with it right? Wonder if I should rethink my idea? How common is the probe issues and is it isolated to just the ph?

I would love to see a pic of your design when you complete it as lately ive been to tap plastics in sf quite a bit lol..