Milwaukee MA887 vs Neptune Conductivity Probe

[NanoTopia]

Hello all,

Hoping to get some feedback from others on this.

I have calibrated my conductivity probe after letting it sit in the sump for 1 week, I believe the conductivity probe is calibrated and working correctly. I also have the temp probe with a conductivity compensation set at 2.1.

I keep my tank temperature at 26c.

I have always kept my salinity based on Milwaukee MA887 digital refractometer at 34.

Now, with the calibrated conductivity probe I get a salinity reading of 31.8 in the tank (also in a cup of water just out of the tank). The reading is stable and not bouncing around, I don't believe there is any interference happening.

That's a difference of 2.2 salinity, and it concerns me greatly.

What do I believe?

The Milwaukee MA887 (which I have checked and re-checked against several salinity standards) or the conductivity probe which I have checked against the Neptune 53,000 standard.

Now the only factor that I can figure may be playing a role in the lower salinity reading from the conductivity probe is the tank temperature (26c). Perhaps the Milwaukee MA887 is not factoring the 26c tank temp.


Any feedback from users of the Milwaukee MA887 and the Neptune conductivity probe or feedback in general would be welcome.

Thank you Christine

[Alain B]

Your Temp probe is connected to the conductivity module ?? If not temperature conductivity compensation must be set to 0.00 .

Here is a procedure to calibrate the cond. probe :

1) Make sure the probe is completely dry (leave out of water for several hours after drying)
2) Prepare water bath at 77F and soak 53,000ms solution to bring up to temp
3) Place PM2 temp probe into water bath and wait till temp stabilizes (adjust temp calibration as required)
4) Start the calibration with dry probe stabilization first. Allow 30 - 60 seconds to stabilize
5) Place probe (hole facing up) in calibration solution and gently shake out any air bubbles. Angle the bag so more solution covers probe end.
6) When finished the reading should be 35ppt or 53,000ms
7) Adjust temp compensation as needed to achieve 35ppt or 53,000ms reading
8) Place probe in tank


Alain

[alb]

I've got the Hanna version of the MA887, but my understanding is that they are the same device. Here are the specs:

http://www.milwaukeetesters.com/MA887.html

Note that the accuracy is +/- 2. That is, your 34 your Milwaukee indicates could in reality be as low as 32 or as high as 36. Such is the nature of methods used to measure salinity; since it's measured only indirectly, precision is always an issue, outside of extremely expensive lab equipment. That being the case, I would be less concerned about the precise value and more concerned about the rate of change.

[NanoTopia]

Your Temp probe is connected to the conductivity module ?? If not temperature conductivity compensation must be set to 0.00 .

Here is a procedure to calibrate the cond. probe :

1) Make sure the probe is completely dry (leave out of water for several hours after drying)
2) Prepare water bath at 77F and soak 53,000ms solution to bring up to temp
3) Place PM2 temp probe into water bath and wait till temp stabilizes (adjust temp calibration as required)
4) Start the calibration with dry probe stabilization first. Allow 30 - 60 seconds to stabilize
5) Place probe (hole facing up) in calibration solution and gently shake out any air bubbles. Angle the bag so more solution covers probe end.
6) When finished the reading should be 35ppt or 53,000ms
7) Adjust temp compensation as needed to achieve 35ppt or 53,000ms reading
8) Place probe in tank


Alain

Thanks for your reply,

Yes I have the temperature probe attached to the PM2 module.

Step 1) from your above directions indicate leaving the probe to dry for several hours, nowhere in the Neptune supplied instructions does it say several hours. I did dry the probe quite well blowing in the holes to rid the probe of water but only maybe 10 minutes. The numbers had settled (-18) for a while.

I feel the probe is calibrated correctly, I replaced the probe in the 53,000 solution after placing it in the tank and got a reading of 53,000.

My question was really about what people thought about the difference between the Milwaukee MA887 results vs the Neptune probe results. If I believe the Neptune probe, my salinity has been low for quite some time (31.8). I keep mainly SPS corals and run a ZEOvit system so I am quite concerned about my salinity being no lower than 34.

[NanoTopia]

I've got the Hanna version of the MA887, but my understanding is that they are the same device. Here are the specs:

http://www.milwaukeetesters.com/MA887.html

Note that the accuracy is +/- 2. That is, your 34 your Milwaukee indicates could in reality be as low as 32 or as high as 36. Such is the nature of methods used to measure salinity; since it's measured only indirectly, precision is always an issue, outside of extremely expensive lab equipment. That being the case, I would be less concerned about the precise value and more concerned about the rate of change.

Thank you for your reply,

I am wondering if it is likely that the MA887 is not compensating for temperature of my sample like the Neptune cond/temp probe is doing (likely more accurately).

Assuming the Neptune conductivity probe is calibrated correctly, would you trust it over the MA887 or Hanna digital refractometer?

[Alain B]

I have 3 different meters , some are compensated for temp and some are not , however they are all reading differently at some point . I rely on the Apex probe exclusively as this had not given me any problems so far . I use the process describe above for calibration and once in a while i just re-test the probe in the calibration solution to check if it had drifted a little . All my corals are happy and growing .

Alain

[NanoTopia]

I have 3 different meters , some are compensated for temp and some are not , however they are all reading differently at some point . I rely on the Apex probe exclusively as this had not given me any problems so far . I use the process describe above for calibration and once in a while i just re-test the probe in the calibration solution to check if it had drifted a little . All my corals are happy and growing .

Alain

Thanks Alain,

So if I place the temp probe in the bath that the standard solution is soaking in then it should be irrelevant what the temperature of the bath is, correct. The temperature of the standard should be compensated for. I keep my tank at 26c, if my bath is at 26c and standard is at 26c, placing the temp probe(compensated for 2.1) in the bath while calibrating the cond probe in 53,000 standard should yield the same results right?


Christine

[Alain B]

I think the compensation number is 2.2 instead of 2.1 but i am not sure about this . I know it is specified in the conductivity module manual . I tried to make sure that when i make my calibration my temp probe is at the same temp as the calibration solution . when i am done i check back the result and if i see a difference i will adjust the temperature compensation a bit to reach 53000 ms . remember that a few 100 of difference in ms only make very little in regards of PPT .

Alain

[NanoTopia]

I think the compensation number is 2.2 instead of 2.1 but i am not sure about this . I know it is specified in the conductivity module manual . I tried to make sure that when i make my calibration my temp probe is at the same temp as the calibration solution . when i am done i check back the result and if i see a difference i will adjust the temperature compensation a bit to reach 53000 ms . remember that a few 100 of difference in ms only make very little in regards of PPT .

Alain

So I have read now that the 2.2 temperature compensation is based on 25c standard temperature. Sounds like it would be more advisable to perform the calibration at 25c rather than 26c with the compensation set to 2.2 as suggested.

The probe is drying now and I will perform a calibration again at 25c using the temp probe in the bath at 25c.

As per your suggestion, I am letting the probe dry longer this time as well.

Also, when performing a salinity check using my digital refractometer I note the temperature is 22.5c at time of reading. Any idea how this would equate to 26c (the temp I keep my tank at)? Is this why there is such a discrepancy between the Neptune probe and the digital refractometer?

[Alain B]

There is some temp compensation chart available , just google for them . Actually i dont let mine dry for a long as i just blow it with a can of compressed air . My digital refractometer read 1.028 when my tank water is set at 53000 cm/sec . Is has always read lower , even my optical refractometer read about the same . However i feel that measuring conductivity is a better way to measure this . If the calibration is good to begin with , the solution is not outdated and the probe is good i am happy.

Alain

PS: I don't run Zeovit cuz i dont have the time for that but my parameters are : nitrates .05 to .1 ppm , phosphates .01 to .02 ppm and all the rest is as per NSW . So basically its the same thing.

[NanoTopia]

There is some temp compensation chart available , just google for them . Actually i dont let mine dry for a long as i just blow it with a can of compressed air . My digital refractometer read 1.028 when my tank water is set at 53000 cm/sec . Is has always read lower , even my optical refractometer read about the same . However i feel that measuring conductivity is a better way to measure this . If the calibration is good to begin with , the solution is not outdated and the probe is good i am happy.

Alain

PS: I don't run Zeovit cuz i dont have the time for that but my parameters are : nitrates .05 to .1 ppm , phosphates .01 to .02 ppm and all the rest is as per NSW . So basically its the same thing.

Okay, I have re-calibrated the conductivity probe in a 25c bath. Results were only slightly different from my previous calibration but nonetheless more accurate possibly.

Also using a Fisher thermometer as back-up on temperature.




So Neptune conductivity probe and temp probe along with Fisher thermometer, bath temp 25c.




So after placing the conductivity probe and temp probe in my sump I get the following reading for 26c (my tank temperature).




My Milwaukee MA887 digital refractometer reads my tank sample salinity at 36, at a displayed temperature of 23.5c.


My conclusion, again assuming the Neptune conductivity probe is correct (within reason), my salinity has been low for more than a year, I figure ~32. I am increasing, very slowly, my salinity to 34 based on the Neptune conductivity probe readings and crossing my fingers. I will be keeping a close eye on corals over the next few days. Nervously I may add.

[Alain B]

Just watch for corals reaction , it should be fine .

Alain


Sent from my iPhone using Tapatalk

[NanoTopia]

Just watch for corals reaction , it should be fine .

Alain




Sent from my iPhone using Tapatalk

Thank you for your help and input

[Alain B]

Ur welcome .

Alain

[zombie]

Why dont you get some 35 ppt calibration fluid and see what ot reads for both the apex and the milwaukee before you start ramping salinity up. It is very possible since they are both digital that both are wrong. Another option is to borrow a friends refractometer calibrated to a 35 ppt solution and see what it reads. Those are by far the most accurate means of measuring salinity outside of lab grade $500 + equipment.

You might be an engineer if...You have no life and can PROVE it mathematically.

[aquamanic]

My conclusion, again assuming the Neptune conductivity probe is correct (within reason), my salinity has been low for more than a year, I figure ~32. I am increasing, very slowly, my salinity to 34 based on the Neptune conductivity probe readings and crossing my fingers.

I would not do that.

Zombie is right - it's possible both are wrong.

Also, if this is a new probe, it needs to sit a little (marinate so to speak) in my experience before you calibrate it.

If your salinity has been wrong, another week or so isn't going to change anything.

[NanoTopia]

Why dont you get some 35 ppt calibration fluid and see what ot reads for both the apex and the milwaukee before you start ramping salinity up. It is very possible since they are both digital that both are wrong. Another option is to borrow a friends refractometer calibrated to a 35 ppt solution and see what it reads. Those are by far the most accurate means of measuring salinity outside of lab grade $500 + equipment.

You might be an engineer if...You have no life and can PROVE it mathematically.

Vertex refractometer ATC calibrated with Pinpoint standard 35ppt /53mS/cm 25c. = 35ppt

Vertex refractometer ATC with home made standard (38g salt with 1L distilled water) = 35.5ppt.

Vertex refractometer ATC measuring tank water = 35ppt

Neptune conductivity probe (calibrated with Neptune standard 53mS/cm) with temp probe (compensation 2.2) = 32.9ppt

Neptune conductivity probe with temp probe (compensation 2.2) in home made standard = 33.0ppt

Neptune conductivity probe with temp probe (compensation 2.2) back in Neptune standard = 34.6ppt ?

Neptune conductivity probe with temp probe (compensation 0.0) back in Neptune standard = 35.3ppt

Neptune conductivity probe with temp probe (compensation 0.0) back in the tank= 33.5ppt

Milwaukee MA887 digital refractometer = 34ppt (33PSU)






Did I miss any possibilities, LOL.


What would you believe or do at this point?

Personally I think the refractometer is out ~1.5ppt as I have read most are. The conductivity probe actually seems more accurate without temperature compensation.

My head is spinning

[zombie]

What does the cond probe read a cup of tank water outside of the tank with temp comp on and off?

You might be an engineer if...You have no life and can PROVE it mathematically.

[NanoTopia]

I would not do that.

Zombie is right - it's possible both are wrong.

Also, if this is a new probe, it needs to sit a little (marinate so to speak) in my experience before you calibrate it.

If your salinity has been wrong, another week or so isn't going to change anything.

Should I trust a refractometer designed for brine (Vertex) over two different digital measurement tools?

The probe has been in the water for over a week now.

Correct, another week will not change anything at this point, are you suggesting I should not trust the Neptune probe and trust something else?

What would you do exactly with the data (in the above post), maybe settle for some kind of happy medium from all the different readings ?


Thanks for your help, I could really use some advice here.

[NanoTopia]

What does the cond probe read a cup of tank water outside of the tank with temp comp on and off?

You might be an engineer if...You have no life and can PROVE it mathematically.

Sorry missed that one, yes I have tested that possibility of interference several times, readings are the same, no change from the numbers I get with the probe in the tank.

[zombie]

What does the neptune probe read when placed in pinpoint calibration fluid?

From the readings I am seeing, one of the calibration fluids is incoreect, which is giving inconsistencies between devices since they have all been calibrated with different fluids. Leave the tank alone for now and pick up a couple 35 ppt packets of milwaukee calibration fluid online somewhere and a bottle from them as well. They are the only "cheap" brand of calibration fluids that I trust. Use that to calibrate your cond probe, and both refractometers, and then repeat the results. If they are within reasonable error between each other (0.5 ppt or less) after that, then I would trust the neptune probes reading and take corrective action to the tank if necessary.

You might be an engineer if...You have no life and can PROVE it mathematically.

[aquamanic]

Nano - 2 articles on this topic that you might be familiar with - if not, there's some good information in them:

http://reefkeeping.com/issues/2006-12/rhf/
http://www.reefkeeping.com/issues/2004-06/rhf/

They explain why you can't calibrate a refractometer with conductivity solution (and vice versa). But beyond just the error in calibration, you're comparing readings from instruments with different accuracy. It's kind of like comparing the temperature from 3 different thermometers each with different accuracy. So what is the 'real' temperature? Nobody knows.

The odds of you finding two different instruments that measure in one unit of measure but display in another, with different levels of accuracy and different calibration methods and get the same answer is small. I think you're just going to make yourself nuts doing what you're doing.

[NanoTopia]

Nano - 2 articles on this topic that you might be familiar with - if not, there's some good information in them:

http://reefkeeping.com/issues/2006-12/rhf/
http://www.reefkeeping.com/issues/2004-06/rhf/

They explain why you can't calibrate a refractometer with conductivity solution (and vice versa). But beyond just the error in calibration, you're comparing readings from instruments with different accuracy. It's kind of like comparing the temperature from 3 different thermometers each with different accuracy. So what is the 'real' temperature? Nobody knows.

The odds of you finding two different instruments that measure in one unit of measure but display in another, with different levels of accuracy and different calibration methods and get the same answer is small. I think you're just going to make yourself nuts doing what you're doing.

I think the truth is somewhere in-between. The refractometers, both digital and optical are not compensating for temperature completely thus giving a higher reading than is actually taking place in the tank due to the fact my reef sits at 26c. The refractometer is calibrated at 20c so when you factor in a 6 degree increase the salinity will naturally drop. The conductivity probe is compensating better for this change in salinity based on temperature and reads the salinity as lower. Makes sense however, I am not fully trusting any of the instruments, but I do favour the conductivity probe. I am going to settle with a salinity 34 indicated by the conductivity probe at this point unless I see anything abnormal happening in the reef.

It seems strange to me that, with all the articles and forum topics I have read on the subject, no one can agree how to properly measure the salinity of a reef aquarium. The theory is clearly in writing but the application is still subjective amongst many. Clearly no one instrument, especially at the hobby level will give an absolute reading of salinity, and I don't expect it to, but we need to develop a better model to at least come close since it is a fairly important parameter for the reef aquarium.

I put trust in my eyes and only time will tell as I raise the salinity slowly now from 33 to 34, first hint of stress I see in corals before 34 and I will know the conductivity probe is incorrect.

I really appreciate all the input everyone and I am open to any other opinions out there on the topic

[t_a_unger]

Thank you all for this very informative and useful discussion -- I'm new to reefing and am suffering through some of the same issues with the disconnect between my analogue refractometer (reads 36) and the Apex Salinity Probe (reads 34). I'll try the temp-neutral calibration method Alain suggested!

Tom

[NanoTopia]

I have learned a lot over the past few weeks regarding conductivity. TRUST the salinity probe "if" you have calibrated it correctly. I now keep my tank at 34ppt (conductivity probe) which reads 35-36ppt on my digital refractometer. If everything looks good in the tank at 34ppt your in range.

http://www.zeovit.com/forums/showthread.php?t=31620