Conductivity Meters: pinpoint vs used lab grade units

[Tim Olson]

Velcro, How do you test the Conductivity? Specifically, do you always take a sample out of the tank and then test it, or do you put the probe directly in the tank? I've found my Pinpoint varies significantly due to flow. For example, today it read 52.1 mS/cm in the refugium, with some flow, and 51.6 mS/cm in a cup of saltwater removed from the tank with no flow. I wonder if the Orion is affected the same way.

I'm pretty OCD on this too, so I would like to get as close to real conductivity as possible.

Thanks

 

[Randy Holmes-Farley]

Velcro, How do you test the Conductivity? Specifically, do you always take a sample out of the tank and then test it, or do you put the probe directly in the tank? I've found my Pinpoint varies significantly due to flow. For example, today it read 52.1 mS/cm in the refugium, with some flow, and 51.6 mS/cm in a cup of saltwater removed from the tank with no flow. I wonder if the Orion is affected the same way.

I'm pretty OCD on this too, so I would like to get as close to real conductivity as possible.

Thanks

There could be other reasons for that, including electrical interference (which is reduced in a 4 electrode design) or temperature effects. I have seen some effects from swirling the electrodes in the water, but generally, the literature says flow should not have a substantial impact on conductivity unless bubbles and such get into the space between the electrode.

 

[Falcon53]

So a couple more questions. I quickly ran through the manual and I am a little confused.

I have the probe 011510. Does this have auto temp comp, or will I need to manually do this?

Are the Pinpoint standards good enough? The Orion ones are over $100! Do you use the Pinpoint salinity standard or conductivity standard?

 

[Randy Holmes-Farley]

The probe does not temperature compensate, the meter does after the measurement, and I'm certain all Orion meters do so.

Assuming it is made as claimed, the Pinpoint solution is fine for checking calibration. There are many other suitable brands as well. Oakton makes a big line of conductivity standards.

 

[Tim Olson]

There could be other reasons for that, including electrical interference (which is reduced in a 4 electrode design) or temperature effects. I have seen some effects from swirling the electrodes in the water, but generally, the literature says flow should not have a substantial impact on conductivity unless bubbles and such get into the space between the electrode.

Thanks ... So it seems the most accurate method would be to test a sample removed from the tank? I also assume the sample should be moved a few feet away to avoid electrical interference (electric fields?).

Also, FYI, I made a 53 mS/cm DIY sample, using your recipe. I scaled it up to 1 liter, since my scale only goes to 0.1 grams. I was very close to the Pinpoint conductivity standard, with the DIY being 52.6 mS/cm. My guess is it was lower, since my Pinpoint standard is a couple of years old and evaporated some. So I recalibrated the Pinpoint to the DIY and will purchase a new standard to confirm.

An Orion is looking more attractive by the minute ...

Thanks again for all the help

 

[reef_ranch]

You stole it from me! Haha. Luckily I was able to find another one

Ha! Glad you found another. I'm playing with it now and either the unit is off or I have been keeping my salinity at 1.0236! Could my refractometer and Milwaukee MA887 be this far off? They both read closer to 1.026.
I did use an opened Neptune 53mS conductivity standard to calibrate the unit. I'll pick up a new standard before making any changes to my tank.

 

[Randy Holmes-Farley]

Thanks ... So it seems the most accurate method would be to test a sample removed from the tank? I also assume the sample should be moved a few feet away to avoid electrical interference (electric fields?).

Also, FYI, I made a 53 mS/cm DIY sample, using your recipe. I scaled it up to 1 liter, since my scale only goes to 0.1 grams. I was very close to the Pinpoint conductivity standard, with the DIY being 52.6 mS/cm. My guess is it was lower, since my Pinpoint standard is a couple of years old and evaporated some. So I recalibrated the Pinpoint to the DIY and will purchase a new standard to confirm.

An Orion is looking more attractive by the minute ...

Thanks again for all the help

When using a probe with built in temperature sensor, measuring outside the tank and away from other electrical devices should be at least as good, and maybe better, than measuring in the tank or sump. Whether it actually makes a difference in most cases, I'm not sure, but it never concerned me enough to measure that way.

 

[Randy Holmes-Farley]

I would also add that the further you are from 25 deg C (the reference standard for conductivity measurements), for measurement or calibration, the more you are relying on the meter to "know" the exact relationship between the conductivity and the temperature and to provide a proper correction.

Since that correction varies with the exact composition of the solution, it is typically just an estimate. You can determine how accurate it is just by taking a cup of tank water out of the aquarium, and monitoring the reported conductivity as the temperature drops to room temp.

 

[Tim Olson]

Thanks!

BTW, per your Oakton comment, I looked at their meters. They sure look nice.

 

[Falcon53]

The probe does not temperature compensate, the meter does after the measurement, and I'm certain all Orion meters do so.

Assuming it is made as claimed, the Pinpoint solution is fine for checking calibration. There are many other suitable brands as well. Oakton makes a big line of conductivity standards.

Yes, I didn't articulate this well. The question should have been:

Does the 011510 probe have the temperature sensor required for the ATC?

The manual indicates that there are probes where an external sensor is required due to the lack of an internal probe.

When using the unit, is the conductivity measure preferable to the salinity measure? The books says salinity is calibrated at 35 for 15C water temp. Sorry...I'm not a chemist so I don't quite understand this.

And I've hijacked the thread!

 

[Tim Olson]

I would also add that the further you are from 25 deg C (the reference standard for conductivity measurements), for measurement or calibration, the more you are relying on the meter to "know" the exact relationship between the conductivity and the temperature and to provide a proper correction.

Since that correction varies with the exact composition of the solution, it is typically just an estimate. You can determine how accurate it is just by taking a cup of tank water out of the aquarium, and monitoring the reported conductivity as the temperature drops to room temp.

Great idea ... I think I'll do that today.

 

[Randy Holmes-Farley]

Yes, I didn't articulate this well. The question should have been:

Does the 011510 probe have the temperature sensor required for the ATC?

The manual indicates that there are probes where an external sensor is required due to the lack of an internal probe.

When using the unit, is the conductivity measure preferable to the salinity measure? The books says salinity is calibrated at 35 for 15C water temp. Sorry...I'm not a chemist so I don't quite understand this.

And I've hijacked the thread!

Its a two electrode model with a temperature sensor:

https://fscimage.fishersci.com/images/D15613~.pdf

What book are you talking about? I'm not sure on any details of how to calibrate your meter (my Orion 128 could not be calibrated), but the reference conductivity will be 25 deg C (or at leas tis today), even if the calibration is performed at a different temp.

 

[Falcon53]

Thanks, Randy. I did try Google but nothing came up unless I totally missed it.

Any insight on the previous conductivity vs salinity measure question? I would hope they would both give the same result!

I'll PM you the manual from Velcro

Second edit:

I can't PM you...if you message me I can reply with the manual.

 

[Randy Holmes-Farley]

In general, conductivity is what the probe measures, and there's no reason to allow the meter to convert it to any other measurement since it doesn't know exactly what the solution is that you are measuring (which alters the conductivity to salinity conversion).

 

[Tim Olson]

I would also add that the further you are from 25 deg C (the reference standard for conductivity measurements), for measurement or calibration, the more you are relying on the meter to "know" the exact relationship between the conductivity and the temperature and to provide a proper correction.

Since that correction varies with the exact composition of the solution, it is typically just an estimate. You can determine how accurate it is just by taking a cup of tank water out of the aquarium, and monitoring the reported conductivity as the temperature drops to room temp.

I've learned a lot since my last post. I took your advice and monitored the reported conductivity at different temperatures. These were the readings:

• 78° 51.1 mS/cm
• 77° 51.2
• 75° 51.6
• 74° 51.7
• 72° 51.9
• 71.5° 52.0
• 71° 52.1

So does this mean the temperature compensation is not fully accurate? Would I be able to apply a correction factor of 0.143 mS/cm per degree F (ΔmS/cm / Δ°F)?

In addition, I also noted dramatic swings in conductivity due to electric fields and virtually nothing due to just flow, as you expected. The conductivity would vary from about 48 mS/cm with me touching the cable when the probe was near a pump or light, to about 52 mS/cm with the sample removed from the tank and away from any electrical interference. Another interesting observation was with the sample away from electrical interference, the reading did not change when I touched the probe wire. I assume this is because there is no field my hand is interfering with, whereas when I have the probe in the tank my hand is interfering with various electric fields, thereby changing the readings. This is awesome, since now I finally know the root cause of the erratic readings I've had.

I assume I'm getting a little OCD on this, but it sure was fun investigating.

Thank you again Randy for your guidance

 

[Randy Holmes-Farley]

The actual uncorrected conductivity declines with temperature declines, so your device is over-correcting.

Given that, I'd calibrate and use it at the same temp (if it can be calibrated), or use it close to 25 deg C. Yes, you can manually correct for temp.

 

[Randy Holmes-Farley]

FWIW, I had a different Orion that had choices for the temp correction algorithm. Does yours?

 

[Tim Olson]

The actual uncorrected conductivity declines with temperature declines, so your device is over-correcting.

Given that, I'd calibrate and use it at the same temp (if it can be calibrated), or use it close to 25 deg C. Yes, you can manually correct for temp.

Thank you ... Thanks for pointing the temp/conductivity relationship, it sure makes more sense to me. I'll recalibrate it at 25°C.

FWIW, I had a different Orion that had choices for the temp correction algorithm. Does yours?

That would be nice, but it states in the manual "The PINPOINT Salinity Monitor is automatically temperature compensated therefore the displayed values are already compensated and corrected." I think I'll contact them, though, and see if there's a way to do it.

Thanks again

 

[Randy Holmes-Farley]

Ah, I didn't realize this was the Pinpoint.

 

[Tim Olson]

Ah, I didn't realize this was the Pinpoint.

Yes, I'm sorry to say it is. It's almost more trouble than it's worth, with the temp correction being off and the significant electrical interference issues.

As I briefly mentioned earlier, I was looking at the Oakton meters, since you mentioned they have good Standards. Is Oakton as good Orion, or is there another brand you prefer (assuming I bought new).

Sorry for all the questions ... but since Salinity is so important, I would like to have an accurate meter, and frankly I don't trust the Pinpoint device.

All the best!