Salinity

[CJO]

It was a little on the expensive side, but I got a Hanna HI96822 digital refractometer for checking my salinity.

Digital Refractometer for Natural or Artificial Seawater Analysis, HI 96822 | HANNA Instruments USA

I had considered getting on of those, but the accuracy doesn't seem to be good enough. It's accurate to +/-0.002. So, if it is reading 1.025, you could have anything from 1.023 to 1.027! That won't be too big of a deal for a fish-only tank, but that's quite a difference for a reef tank.

CJ

 

[davework]

I have a basement sump and use the refractometer. No issues under CFLs for me.

 

[Munch]

Reviving old topic...

Hi I just ordered and received the BRS ATC optical refractometer, and calibration fluid.

Instructions say to calibrate with RO/DI water, and when I do, it does match readings I get with my digital Hanna refractometer. This is good.

However, when I then test the calibration fluid, it’s reading is 1.028 on both optical ATC and digital Hanna. That's bad, why doesn't it read 1.026?

So, my dilema is, which is correct?

Seems like the calibration fluid is off. Since both the ATC and Hanna read the same saltwater the same. But I can’t believe the calibration fluid is off.

BRS online instructions say to calibrate with the calibration fluid.



I bought the ATC optical to double check my Hanna, but with the odd results I get, I’m not sure what’s off, BOTH my new ATC AND Hanna, or just the calibration fluid.

Or am I running into the issue that calibrating with RO/DI 0 TDS result in + .002 off reading at 1.026 measurements?

It's super frustrating, as I'm trying to know exactly what my salinity is.

 

[Mike&Terry]

...Or am I running into the issue that calibrating with RO/DI 0 TDS result in + .002 off reading at 1.026 measurements?

My bet would be on this.

 

[Munch]

Ok, I believe the issue with using a Hanna is the fact it is calibrated with RO/DI water 0 TDS.

I grabbed a second independent 1.026 calibration fluid 53 mS/cm with refractive index of 1.3394

When I calibrate my optical ATC unit (with either calibration fluid), it does reads both solutions at 1.026, which is good. When I drop each of these calibration fluids onto the Hanna, the Hanna reads both at 1.028.

So the bottom line is the Hanna unit will always (consistently it seems) read your salinity .002 high, as it was calibrated with RO/DI 0 TDS water.

I'm honestly shocked you cannot calibrate the Hanna with calibration fluid, seems like a serious flaw in their design.

 

[fragmatic]

I think I read somewhere that the Hanna digital salinity testers measure salinity by conductivity. Salt makes water conduct electricity. Pure water does not conduct electricity, and therefore RODI water at 000 does not conduct electricity. Our TDS are also conductivity meters calibrated to read PPM. So using RODI to do the calibration makes since in that context. The thing that makes me do a think is that other impurities cause water to conduct electricity also. We add trace elements to our water. So they must effect the accuracy, IF I am correct. The refractometer measures salt content by refraction, and the swing arm measures specific gravity or the gravitational weight. However the swing arms are prone to all kinds of problems, such as deposits, friction, temperature, wear, bearing slop, and salt grit & trace elements binding in between the bearing surfaces.

It is my understanding that the refractometer method is the most accurate for a reasonable price, and the digital conductivity meter method is the next most accurate but more simple to operate. I do not have a Hanna yet but plan to get one at some point and intend to calibrate my refractometer with the standard fluid provided then test a sample of tank water with it and then with the Hanna and to then calibrate the Hanna per the refractometer reading AND RODI water to see if they agree. If they do not I will then use the reading off the refractometer to calibrate the Hanna BECAUSE it is what I have been using and running my tank by. This does not mean I think the Hanna is wrong it just means I will use it for being handy and to keep my water the way it is currently.

That is a lot of mumbo jumbo.

In fact, I just logically talked myself out of buying a digital salinity meter and will stick with my refractometer.

 

[Mr Beardsley]

I think I read somewhere that the Hanna measure salinity by conductivity. Salt makes water conduct electricity. Pure water does not conduct electricity, and therefore RODI water at 000 does not conduct electricity. Our TDS are also conductivity meters calibrated to read PPM. So using RODI to do the calibration makes since in that context. The thing that makes me do a think is that other impurities cause water to conduct electricity also. We add trace elements to our water. So they must effect the accuracy, IF I am correct. The refractometer measures salt content by refraction, and the swing arm measures specific gravity or the gravitational weight. However the swing arms are prone to all kinds of problems, such as deposits, friction, temperature, wear, bearing slop, and salt grit & trace elements binding in between the bearing surfaces.

It is my understanding that the refractometer method is the most accurate for a reasonable price, and the digital conductivity meter method is the next most accurate but more simple to operate. I do not have a Hanna yet but plan to get one at some point and intend to calibrate my refractometer with the standard fluid provided then test a sample of tank water with it and then with the Hanna and to then calibrate the Hanna per the refractometer reading AND RODI water to see if they agree. If they do not I will then use the reading off the refractometer to calibrate the Hanna BECAUSE it is what I have been using and running my tank by. This does not mean I think the Hanna is wrong it just means I will use it for being handy and to keep my water the way it is currently.

That is a lot of mumbo jumbo.

In fact, I just logically talked myself out of buying a digital salinity meter and will stick with my refractometer.

Hanna makes both a digital refractometer Digital Refractometer for Natural or Artificial Seawater Analysis, HI 96822 | HANNA Instruments USA and a conductivity meter pH/Conductivity/TDS Tester, HI 98130 | HANNA Instruments USA. I think the refractometer is what most people refer to when talking about the Hanna.

 

[fragmatic]

Hanna makes both a digital refractometer Digital Refractometer for Natural or Artificial Seawater Analysis, HI 96822 | HANNA Instruments USA and a conductivity meter pH/Conductivity/TDS Tester, HI 98130 | HANNA Instruments USA. I think the refractometer is what most people refer to when talking about the Hanna.

I think you are right. I will edit my post to say Hanna digital where it is applicable. Thank you for the heads up.