Stray voltage, pH drop, fan problem (any EE's around?)

[Colin]

Here's a good one.

Every day between around 2pm and midnight my Reef Angel controller shows a drop in pH from normal 8's to less than 6. I know it's not really dropping as my tank isn't dead and my Seneye doesn't register the drop. Reef Angel controllers will show a drop in pH with stray voltage in the tank, so I believe there may be some voltage coming from somewhere.

I have a fan blowing across the sump when the water temperature rises and the pH drop correlates with the fan being on. It isn't an instant drop, it is gradual and rises gradually after the fan goes off. It takes a few hours to get the the upper 5's where it levels out, and about the same time to rise to normal. I can reproduce the problem by turning the fan on and off manually. I do not get the drop with the fan on and NOT blowing across the water.

So what's going on? Fan causing a static buildup somehow? I put in a grounding probe (plugged into a power strip, problem?) with no effect.

Any thoughts or theories would be greatly appreciated.

--Colin

 

[Fish Keeper82]

Is the fan an ac or dc fan?

Is the fan cable routed with the ph wire?

When you tested the fan not blowing on the water surface to see ph response, did the cables move from each other significantly?

 

[Colin]

It's an AC clip-on fan. The power cable isn't routed with the pH probe wire. I essentially just rotated the fan head away from the water so there wasn't any cable movement and at that point the cables are a couple of feet away from each other.

Thanks,

--Colin

 

[Fish Keeper82]

It's an AC clip-on fan. The power cable isn't routed with the pH probe wire. I essentially just rotated the fan head away from the water so there wasn't any cable movement and at that point the cables are a couple of feet away from each other.

Thanks,

--Colin

The only thing i can think of is some stray magnetic induction from the AC motor. You say its a clip on ...what happens if you suspend the fan higher from the surface? If it is magnetic induction is should be significantly reduced if the fan is higher. Try it and see. That could be why rotating fan head works if the magnetic lines of flux change direction.

 

[Colin]

I raised it about 6" and turned on the fan. I'll have some results shortly.

It's also near one of my drain lines, so if this doesn't fix it maybe I can move it away from there.

Thanks!

--Colin

 

[Benson0219]

FYI. My grounding prob says not to plug into a power strip.

 

[Colin]

Moved away from drain line, higher up, still dropping. I'll try plugging the ground probe into an outlet.

--Colin

 

[smmiller506]

It might not be the fan that's at issue here, it may be the pH sensor at fault. Can you move that to a different location?

Also, try plugging the fan into a different circuit of the house (use an extension cord if necessary for testing purposes.

 

[sleepydoc]

I agree with fishkeeper-

It sounds like you have some electrical interference between the fan and the pH probe. pH probes work by sensing a voltage induced on the glass electrode in response to pH. It's a relatively small voltage, so it wouldn't take much to cause an error. My guess is that the shielding on the probe or cable may be bad so the fan is causing an induced charge that slowly builds up over time.

Try moving the fan to the other end of the sump and see what happens. If you're really industrious, you can take the blades off the fan, leaving it in place, so the motor and any EMF it produces are unchanged, there is no air movement. Turn it on and see what happens. Then move the fan and/or rotate it and monitor any changes.

 

[Colin]

I've moved the pH probe from the middle of the sump to the far end, so the fan is on one end of a 40B and the probe is at the other end. I'll watch it and see how it does. I'll try some of the other suggestions on Monday when I have some free time.

--Colin

 

[ericarenee]

Do you have a Volt meter.. Your POWER Strip or the wall socket your using seems to have a Floating ground and the static current from the fan is NOT being pulled thru the ground could be another issue.
You can test your outlet with a volt meter..I could explain to you how to do so. But would prefer you go to youtube and search how to test a outlet. there are some videos up there with step by step. I would not want to get you shocked...

 

[salty joe]

Not familiar with Reef Angel, but do know that PH monitors can be touchy. I decided to use a 9V wall wart to power my Pinpoint PH monitor and was getting all kinds of weird numbers and it threw me as it was in a brand new setup. For the heck of it, I installed a 9V battery-problem solved.

 

[Colin]

It's a well documented "feature" . Stray voltage causes the pH reading to drop. Usually, it's a significant drop to 1 or 2. It's actually kind of handy sometimes.

 

[Icefire]

Look for a cut in the probe rubber

 

[Colin]

Outlet checks out OK. I tried another outlet on another circuit for the grounding probe as well as a true earth ground and neither helped.

And the winner is...

Bad pH probe! Swapped it out with an extra and it's not dropping. It's reading 8.58, but it's not dropping. Time to order a new probe.

I'm still not sure what was going on with the original probe. Such a strange problem.

Thanks to everyone who replied!

--Colin

 

[Angry Andy]

Glad you found it....

Any signs of exposed wiring or probe cracking?

 

[Colin]

Nothing obvious.

I'm still baffled as to why it only occurred when the fan was blowing on the water, and even with a grounding probe installed.

--Colin

 

[Icefire]

Probably a bad shielding

 

[sleepydoc]

Nothing obvious.

I'm still baffled as to why it only occurred when the fan was blowing on the water, and even with a grounding probe installed.

--Colin

Yeah. That was confusing me, too. I agree with the bad shielding theory. Like I said, they measure very small voltages, so bad shielding or a poor connection of the shielding at the housing could cause it. Glad you figured it out!