Contradicting salinity results

[Randy Holmes-Farley Verified Community Expert]

Hi Randy, just so you are aware of my lack of knowledge of chemistry, when reading your reply you lost me at EDTA, ha ha.

I did some reading on conductivity in liquids along side my basic knowledge of conductivity of elements from the periodic table. I see what you mean by such a large drop (10%) I think for lay persons like myself the interchange between ppt and ppm can easily be misleading if one is not careful.

As Hans-Werner commented that this is only an observation and not a detailed theory. I thought I would add my observation. When you first mix the salt (Only Bio Active) the salt appears to dissolve at about the same rate as the Pro Reef. However the Bio Active salt does seem to be slightly more opaque for a longer period. This seems to dissipate after a while (overnight). I wonder if any bonding agents are delaying the salts from dissolving completely during the activation of the Bio elements.

I must point out this is not a theory just an observation. As the only additional element of Bio Active over Pro Reef that I am aware of is the organics. I would assume this is what is driving the observation.

Thanks for sharing your knowledge Randy, as always you have instilled a little more knowledge in myself and a whole lot more questions for me to study. I will leave the conversation for others to add their comments and follow with interest.

Best wishes.

I can certainly accept that the salt may not be fully dissolving as quickly as other salts, and if you try to measure salinity by conductivity before it dissolves (i.e., while cloudy with undissolved salt, say 10% of the total salt mass is still undissolved) you'll get a false reading while a hydrometer will still "count" the mass of the undissolved solids.

The explanation of binding the ions or making gel globs that are both unconductive is what I reject.

Sorry about switching units around fast. The relationship between the various units (ppt, mS/cm, ppm of calcium bound up, etc.) doesn't lend itself to a simple discussion.

 

[Tony Thompson]

Hi @Night Reefer , sorry for the slight detour.

Hope you find an explanation for your discrepancy between refraction and conductivity. I will follow with interest.

Did you by any chance try measuring a sample of your water outside the aquarium, Just to count out any interference? Obviously at the same temp as your DT. I sometimes float a small beaker in my rear sump with the test sample, just to make sure they match in temp.

 

[MJNTWise]

Never ever trust the salinity probe....

 

[Randy Holmes-Farley Verified Community Expert]

Never ever trust the salinity probe....

lol

FWIW, it's what chemical oceanographers use to measure salinity, but they don't use aquarium controllers hooked to them.

 

[chefjpaul]

lol

FWIW, it's what chemical oceanographers use to measure salinity, but they don't use aquarium controllers hooked to them.

Im quite sure they take care and calibrate their equipment..... unlikely that many reefers to as frequently as needed.

 

[Tony Thompson]

Im quite sure they take care and calibrate their equipment..... unlikely that many reefers to as frequently as needed.

I much prefer my Conductivity meter over a refractometer

It gives me a clear digital readout and I can measure directly within the water at my reference temp of 25c. So don`t` have to rely on ATC to compensate. (unless the temp of the sample is different than the cal temp) I agree that all equipment including refractometers need to be properly cared for and calibrated. But a simple wipe with RODI is all that is required with a Conductivity probe. If you see a reading that seems a bit odd, just check against a reference.

I think some of the problems encountered by reefers may be compounded by:

Not taking seriously the effects of temperature. Important for Refraction, Conductivity and Specific Gravity.
Using a calibration fluid not designed for the specific measurement.
Using measuring equipment that was not specifically manufactured for the task.

Last but not least, if you are anything like me, just plain user error, ha ha.

 

[Night Reefer]

G

Best is as I do when in question to jot down your reading, take a sample to your local LFS and also take a reading via refractometer and see what you results are via all 3 sources.

Been real busy getting the taxes done. Great idea will stop by tonight and pick up some water. I will also test mine in a sample cup.
Post the results tonight

 

[Night Reefer]

Watched a late night video before falling asleep with one eye open. Neptune even says that the probe in the refractometer will have different results due to the ions in the water.
It was with Neptune and Reefdude here is the link.

 

[Tony Thompson]

Watched a late night video before falling asleep with one eye open. Neptune even says that the probe in the refractometer will have different results due to the ions in the water.
It was with Neptune and Reefdude here is the link.

You know when you mentioned that this was going way of topic. That is exactly what we were discussing. Without any ions the conductivity would be Zero. That is why your DI (De Ionisation Resin) in your RODI unit can produce Zero TDS. The ions are the salt, calcium, Magnesium etc. Without them you just have DI water, not sea water.

Once again I would strongly recommend you get a reference solution of NSW. Many available at very low cost. The only positive way to check calibration. But don`t` forget to compensate for temp. Floating a beaker of reference solution in the tank water will give a temp equilibrium.

Not sure how the Apex calibrates against temp in the calibration solution. I would have thought it uses the Temp probe. But if the temp probe is in the DT and the cal solution is outside the tank water, there will be a discrepancy in calibration dependant on the difference in room temp and DT temp. Most cal solutions are set at 25c some are at 20c so always best to check that the solution temp is on point or near.

interesting to hear the comments on the video about devices calibrated at 25c rather than 20c. The reason some are set at 20c is because this is the average room temp. If you take 25c water from your tank and place it on a refractometer that has been sat at room temp (say 20c) then that very small body of water is very quickly going to find equilibrium with the room temp. Now you are measuring the refraction of salt water at 20c not 25c.

Five degrees celsius deviation If I remember correctly can give a reading difference of 2 ppt. Even though the salinity has not actually changed. This would be in reference to Density change with temp. Not sure what the deviation is with refraction. But they all reference one another. 35ppt, 1.026, 53 mS/cm (all at 25c)

 

[Randy Holmes-Farley Verified Community Expert]

Watched a late night video before falling asleep with one eye open. Neptune even says that the probe in the refractometer will have different results due to the ions in the water.
It was with Neptune and Reefdude here is the link.

Thanks for posting that video. I listened to the first 46 min, then it seemed to go off topic, but it was generally good. I did think the temperature effect and compensation for conductivity could have been explained a lot better. “Smoothing out” the effect doesn’t leave folks with any useful understanding of the effect and how it is corrected for, and understanding why the APEX may get it wrong. [emoji3]

 

[Tony Thompson]

BRS TV to the rescue. Now I understand how the Apex probe is calibrated via a reference temp. Nice one BRS TV.

https://www.bulkreefsupply.com/vide...ex-Aquarium-Controllers-from-Neptune-Systems/

 

[Tony Thompson]

I like this guy, old school like me, ha ha. Excellent tip to make sure all the bubbles are out of your conductivity probe and keep the probe at temp during calibration.

 

[Night Reefer]

Did a test in a cup and the results were the same. (.2 off) not a big deal. I recalibrate again and it still read high. Over time ( the last week) the probe numbers started falling. Why I don’t know. The Refractometer and the probe are almost exactly on. Only problem is my levels are a bit too high 36.3 so I will have to do a small water change to bring the numbers down. Can anybody understand why it took this long for the two numbers to level off? The salt was placed in my sump with high water flow. One thing I was told by Neptune/apex was that I should not use the The temperature offset sometimes it will throw the numbers off but this was not in play for this scenario.

 

[Randy Holmes-Farley Verified Community Expert]

I’m not a fan of conductivity as implemented by controllers. It seems very prone to issues that just do not seem to arise with stand alone conductivity meters.

 

[Stigigemla]

They are sensitive to electrical interference.
First you need a ground probe in the sump. A titanium heater with ground connector is super.
Second they dont work well with mains electrical cords near the probe.