Contradicting salinity results

[Night Reefer]

The refractometer and reference solution is from BSR calibrated using the calibration solution which is 35 PPT at 53.0ms.

The salinity probe is the apex Neptune that came with the system and was calibrated twice the last time with a apex technician using their reference solution.

First thing I did was calibrate the refractometer. Then I cleaned it with ro water and then put a sample of a tank water. My numbers are off by more than 2 points.

I checked for micro bubbles on the salinity probe by tilting it and shaking with no change.

I just need to establish a reference point of 35. If I use the apex as the reference and it’s wrong my swing could be 36 to 38 PPT if it’s correct no problem. If I use the refractometer it’s off and the apex is correct on my swing can be 31 to 33. So what I’m trying to say is my numbers would be between 31 & 38 which 31 is too low and 38 is too high. I also know consistency is the key and I don’t mind being off but I think this is just a bit too much.

Just had my lights come on.

As a test tonight I’m going to open up another bag of reference solution from Apex stick the probe in there and see if I get 35 I am also going to take some droplets from the same reference and see if I get 35 on the refractometer. If I get the same results then I know that I am getting some interference on the probe when it’s in the water. If I don’t at least I will know which device is off.

Tony T np it happens

 

[Night Reefer]

If you used a perfectly made salt refractometer (most are) and calibrated perfectly with ro/di, it WILL read 1.7 ppt too high in seawater . That sounds like it matches your current variance fairly well.

Can you elaborate a bit on this because I was always told never to use RO water to calibrate

 

[Randy Holmes-Farley Verified Community Expert]

The refractometer and reference solution is from BSR calibrated using the calibration solution which is 35 PPT at 53.0ms.

The salinity probe is the apex Neptune that came with the system and was calibrated twice the last time with a apex technician using their reference solution.

First thing I did was calibrate the refractometer. Then I cleaned it with ro water and then put a sample of a tank water. My numbers are off by more than 2 points.

I checked for micro bubbles on the salinity probe by tilting it and shaking with no change.

I just need to establish a reference point of 35. If I use the apex as the reference and it’s wrong my swing could be 36 to 38 PPT if it’s correct no problem. If I use the refractometer it’s off and the apex is correct on my swing can be 31 to 33. So what I’m trying to say is my numbers would be between 31 & 38 which 31 is too low and 38 is too high. I also know consistency is the key and I don’t mind being off but I think this is just a bit too much.

Just had my lights come on.

As a test tonight I’m going to open up another bag of reference solution from Apex stick the probe in there and see if I get 35 I am also going to take some droplets from the same reference and see if I get 35 on the refractometer. If I get the same results then I know that I am getting some interference on the probe when it’s in the water. If I don’t at least I will know which device is off.

It is disappointing to me how many people have issues getting correct conductivity and pH readings from controllers, probably due to complexities relating to the temperature calibration and compensation.

My bet is on the refractometer being correct, but if right now you test both methods with the same standard solution, what do you get?

Remember, the APEX needs to either measure the temp of the calibration solution, or it needs to be at the same temp as the tank water (where the temp probe might still be).

Also, can you link the exact solution you have?

Standards that are 35 ppt for a conductivity meter (53 mS/cm) do NOT need to be 35 ppt for a refractometer. My DIY, for example, is different.

 

[Night Reefer]

It is disappointing to me how many people have issues getting correct conductivity and pH readings from controllers, probably due to complexities relating to the temperature calibration and compensation.

My bet is on the refractometer being correct, but if right now you test both methods with the same standard solution, what do you get?

Remember, the APEX needs to either measure the temp of the calibration solution, or it needs to be at the same temp as the tank water (where the temp probe might still be).

Also, can you link the exact solution you have?

Standards that are 35 ppt for a conductivity meter (53 mS/cm) do NOT need to be 35 ppt for a refractometer. My DIY, for example, is different.

Will let you know tonight if I get home before dark if not it will be tomorrow night

 

[Tony Thompson]

Hi Gareth, I have heard this suggestion with the Neptune Apex probe somewhere else on the forum. That is why I suggested earlier that the probe be tested in a fresh salt mix outside the tank.

I don`t have an Apex, what type of probe is it. Is it a four pole probe with shroud?

 

[Night Reefer]

I think 2 pole but not sure

 

[Night Reefer]

Well this kills my idea
https://www.reef2reef.com/threads/w...meter-conductivity-meter.366337/#post-4528130

 

[Night Reefer]

Wonder wonder wonder, can I use sea water? I live in Florida. It would be a good way of checking the Refractometer???????

 

[Breadman03]

Wonder wonder wonder, can I use sea water? I live in Florida. It would be a good way of checking the Refractometer???????

Seawater salinity varies, particularly near the shore where rivers and rainwater are mixing with the main body of water. I’m in landlocked PA, but some FL folks probably have better insight.

PS: I was shoveling snow this morning.

 

[Randy Holmes-Farley Verified Community Expert]

Wonder wonder wonder, can I use sea water? I live in Florida. It would be a good way of checking the Refractometer???????

No, you have no way to know the salinity. 35 ppt is a whole ocean average, but it varies a lot depending on local conditions.

 

[Gareth elliott]

Might get you in the ball park but not sure its going to get you exactly 35ppt. I recently tested my nsw, i live in a shore town in nj. I got a reading of 1.021sg on a calibrated refractometer. Theres a river that enters nearby explaining the lower salinity.

 

[Night Reefer]

Well that one is out the door

 

[Randy Holmes-Farley Verified Community Expert]

It is easy to make standards for salinity calibration:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-06/rhf/index.htm

 

[Stigigemla]

Stray voltage can cause probes to read almost any value. A ground probe usually will handle this.
But there is a simple way to check this. Just take a glass of tank water. Place it on a plastic sheet and measure it.
Stray voltage will not go through the plastic sheet so if you get another reading it should be stray voltage in your sump.

 

[Tony Thompson]

Hi, I have heard this statement before about stray voltage in the tank being blamed for discrepancies in conductivity readings.

However the circuit design in a decent 4 pole conductivity meter would suggest to me that this should not be the case. The circuit uses a reference voltage fed back through the circuit for potential at a predetermined frequency. The four poles are positioned in such a way and the shroud is included to stop any electromagnetic field effects. That is why those cheap (Icecap salinity probes) two pole salinity meters use a small cup to measure in. They seem to be more like a simple TDS meter to me.

I am unaware of the tech spec of the Apex probe, so I do not know if it is capable of being altered by interference from stray current. The majority of aquariums will have electromagnetic interference. Simply by the nature of the Electrical devices used. Lots of inductive loads. I would find it very disappointing if these relatively small field effects would make your probe inaccurate.

Like I mentioned earlier. there is a very simple way to test this. Just use the probe in a bucket with your salt in it and see if their is a difference.

With regards reference solutions. I would suggest using a NSW reference solution such as Accurasea, Fauna Marin or ATI. These can be used as reference but I am aware that certain manufacturers advise that for calibration a particular solution be used.

 

[Tony Thompson]

Just on a separate note @Randy Holmes-Farley. I received an answer back from Hans-Werner Balling (Tropic Marin) with reference their instruction re 10% deviation in conductivity of their Bio Active Salt.

"Thank you for discussing our products in this forum. we much appreciate it.

Thank you, I had a great spring break, hope you too.

We found that the organic substances in our Bio-Actif may reduce conductivity when we checked freshly prepared saltwater with the proper amount of salt for its conductivity. Since some of the organic additives are complexing and gelling agents we think this may reduce conductivity of the saltwater by altering charge and movement of ions. We have no more detailed theory on this observation.

Kind regards

Hans-Werner Balling"

Very kind of him to give such an immediate and honest reply. Thank you Hans-Werner, and well done Tropic Marin.

 

[Tony Thompson]

I think 2 pole but not sure

You would normally be able to remove the shroud for cleaning. This is a picture of my Hanna Probe on my Meter just for your reference.

 

[Randy Holmes-Farley Verified Community Expert]

I appreciate their reply, but do not believe it to be true that a small amount of organic that might be in bioactif can have that effect. Even if you added a hugely whopping 100 ppm of organic matter, and that bound up and made an equal amount of ions totally nonconductive, you take out 100 ppm from 35,000 ppm. No way does that account for a 10% drop.

Imagine adding EDTA to bind calcium and make it nonconductive. It binds about 1/5th of it’s weight in calcium.

There’s just no way any small amount of organic matter can take out 3,500 ppm of conductive ions from seawater.

 

[vetteguy53081]

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.

 

[Tony Thompson]

I appreciate their reply, but do not believe it to be true that a small amount of organic that might be in bioactif can have that effect. Even if you added a hugely whopping 100 ppm of organic matter, and that bound up and made an equal amount of ions totally nonconductive, you take out 100 ppm from 35,000 ppm. No way does that account for a 10% drop.

Imagine adding EDTA to bind calcium and make it nonconductive. It binds about 1/5th of it’s weight in calcium.

There’s just no way any small amount of organic matter can take out 3,500 ppm of conductive ions from seawater.

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.