Salinity Monitor discrepancy

[ccurnick]

I received my salinity monitor today from you guys and I believe there is an issue. My tank registers at 1.026sg with my refractometer, and everything in my tank is doing great.

I calibrated my new monitor and it was registering my tank at 30.4ppt, obviously way out of the acceptable range for a reef and way off of my other reading. I then used the calibration fluid to calibrate my refractometer, which read the fluid as very low, up to 35ppt. I then measured my tank again and it came out to 1.032 sg. I repeated this with another pack of the fluid that I ordered separately, and got the same results.

I am thinking my monitor is off, anyone have any ideas/ran into this?

 

[Saluqui]

I have. I just received mine last week. It seems to be reading way low. I have calibrated it twice. I also have an expensive refractometer which I have calibrated. I trust the refractometer. The Hannah checker is off...

 

[Hanna Instruments]

Thanks for reaching out.

Two of the most popular ways to measure salinity for aquariums are refractometers and conductivity meters. Our HI96822 digital seawater refractometer is used to measure salinity via refractometry while our HI98319 waterproof salinity and temperature meter measures salinity via conductivity.

What is refractometry?

With our HI96822 salinity determinations are made by measuring the refractive index of seawater. Refractive Index is an optical characteristic of a substance and the number of dissolved particles in it. Refractive Index is defined as the ratio of the speed of light in empty space to the speed of light in the substance. A result of this property is that light will “bend”, or change direction, when it travels through a substance of different refractive index.

What is conductivity?

Conductivity is most commonly defined as a substance’s ability to transmit heat, sound, or electricity. Small charged particles called ions help to carry the electrical charge through a substance. These ions can be positively or negatively charged. The more ions available the higher the conductivity; fewer ions will result in lower conductivity. Also, the higher the conductivity, the higher a solution’s ability to conduct electricity. This is a result of a large number of charged ions present in the solution. Since the various elements used to make up salinity carry an ionic charge, conductivity is used to determine their gross concentration in water.

What is better for salinity?

When comparing conductivity to refractometery to measure salinity, the consensus among the scientific community favors conductivity. This is because there are non-conductive material which can impact the refractive index of seawater but not the actual salt concentration. For example, if we add sugar to artificial seawater, we will see that our salinity value will increase but we have not changed the concentration of salt in the water. If we measured the salinity of that sample with our HI98319 conductivity meter you’ll notice the value is largely unchanged. It is common to have inflated values with a refractometer due to the large number of materials which will affect the density of that water outside of the dissolved salt values. For example, organic waste, sugars, potential non-ionic contaminants or uneaten fish food can increase the values produced on a refractometer but this would be less likely to occur on a conductivity meter like the HI98319.

Important Information about our HI98319

1. You cannot use the calibration solution for refractometers. The calibration solution is a 35ppt conductivity standard based off of the International Oceanographic Tables
2. The calibration solution is a one time use and cannot be reused after calibration

 

[Hanna Instruments]

I have. I just received mine last week. It seems to be reading way low. I have calibrated it twice. I also have an expensive refractometer which I have calibrated. I trust the refractometer. The Hannah checker is off...

If you are measuring salinity with an optical refractometer you have to measure the water the the temperature to which it is calibrated to. Optical refractometers have a really narrow temperature range for calibration and if your water is not the same temperature as the what your refractometer is calibrated to then you can get different results. Our new salinity tester directly measures the water temperature and compensates for any difference.

 

[Hanna Instruments]

 

[Hanna Instruments]

I received my salinity monitor today from you guys and I believe there is an issue. My tank registers at 1.026sg with my refractometer, and everything in my tank is doing great.

I calibrated my new monitor and it was registering my tank at 30.4ppt, obviously way out of the acceptable range for a reef and way off of my other reading. I then used the calibration fluid to calibrate my refractometer, which read the fluid as very low, up to 35ppt. I then measured my tank again and it came out to 1.032 sg. I repeated this with another pack of the fluid that I ordered separately, and got the same results.

I am thinking my monitor is off, anyone have any ideas/ran into this?

what is the accuracy statement of the refractometer you are using?

 

[Saluqui]

Yes, I understand all that you mention in your reply, but the fact remains you instrument is reading low.

 

[Hanna Instruments]

I have. I just received mine last week. It seems to be reading way low. I have calibrated it twice. I also have an expensive refractometer which I have calibrated. I trust the refractometer. The Hannah checker is off...

what is the accuracy statement of your refractometer?

 

[Saluqui]

I have used refractometers for years. I have 2 from 2 different manufacturers. They are calibrated correctly (temp) and are reading exactly 35 ppt, while The hannah is reading 33.5

 

[Hanna Instruments]

I have used refractometers for years. I have 2 from 2 different manufacturers. They are calibrated correctly (temp) and are reading exactly 35 ppt, while The hannah is reading 33.5

what is the accuracy statement of your refractometer?

 

[Saluqui]

 

[Hanna Instruments]

I have used refractometers for years. I have 2 from 2 different manufacturers. They are calibrated correctly (temp) and are reading exactly 35 ppt, while The hannah is reading 33.5

We have an accuracy statement of ±1 ppt for 0.0 to 40.0 ppt; ±2 ppt for readings over 40.0 ppt (@25ºC/77ºF)

When you factor in the accuracy statement of both meters they are aligned. Your refractometer is probably picking up anti caking agents in salt or some other none ionic solution which is causing a higher reading in the refractive index but not actually in the salt concentration (i.e salinity value).

 

[Saluqui]

For 2 different refractometers? I don't buy it