Salinity has been off???

[Nick Rose]

I have been using the Hanna Salinity tester for over a year but I also compare it to my calibrated refractometer. Well I decided to get new calibration fluid since the other one is two years old. Surprise, Surprise it has been off. It now shows the tank is at 38-39ppt. So I decided to calibrate the Hanna and that is showing 36.5ppt. I also had a local LFS test it with their refractometer. Also had a local reefer with a Hanna check it and his matched my Hanna. I also bought two other refractometer calibration fluids and they matched the other new bottle. Both tanks have been running at 38-39ppt for possibly a year or less. Everything is looking great especially SPS I have gotten from a local reefer in December and end of February. All of his is encrusting nicely. You would think that his SPS would have died going from his 35ppt tank to my 38-39ppt tank.

Here is the question. Should I follow Hanna or Refractometer. Both have a accuracy of +/-1ppt. If I go by the refractometer should I drop it down 1ppt and wait a few months and if everything looks fine drop it down another 1ppt and so forth until I’m down to 35ppt.

The picture is a Shag Priority I got on February 27 and the second is it on April 8th.

 

[Suohhen]

Is it an auto correcting refractometer? It seems the Hanna is correct but regardless your a bit high so you can being dropping it down and 1ppt a week is certainly fine. What I do when I add coral is check the salinity of both since it is most important that they are the same regardless of what the true reading is.

 

[Nick Rose]

Is it an auto correcting refractometer? It seems the Hanna is correct but regardless your a bit high so you can being dropping it down and 1ppm a week is certainly fine. What I do when I add coral is check the salinity of both since it is most important that they are the same regardless of what the true reading is.

If your talking about auto correcting for temperature then yes.

 

[Suohhen]

If your talking about auto correcting for temperature then yes.

What is the salinity of the calibration fluid?

 

[Nick Rose]

The bottles are 35ppt.

 

[Suohhen]

Strange. So you calibrated to 35ppt and then immediately got a reading of 39 with your refracto? That is pretty compelling.

 

[Suohhen]

Refractometers are sensitive, it could be that it isn't holding its calibration, the glass is dirty or scratched, there is some contamination or misalignment inside. Regardless everything is pointing to the Hanna being correct so I'd buy a new refractometer.

 

[coralfishreef]

I recommend the Tropic Marin high precision hydrometer. Unless you’re prone to break delicate equipment.

I use the hydrometer to check and calibrate the refractometer every week or two.

 

[Nick Rose]

In my post I also mentioned I had a LFS test my water and there’s matched my refractometer. I also just tested with a fellow reefers refractometer and it matched mine. So all three refractometers which are all calibrated are showing my tank water at 38-39ppt. I doubt all three refractometers are broken. I might try and find 1 or two more people with refractometers to test.

 

[Suohhen]

Here is the top question on Amazon for the Hanna Checker.

 

[Suohhen]

And the top three reviews all give 1 star for inaccurate readings.

 

[Nick Rose]

I guess I could always buy the Tropic Marin high precision hydrometer and see where that reads to tell me which one is correct or closer.

 

[Suohhen]

I guess I could always buy the Tropic Marin high precision hydrometer and see where that reads to tell me which one is correct or closer.

It is hard to imagine a 3 refractometers are wrong and you are seeing exactly what the person on Amazon is saying so it seems open and shut that you can trust your refact.

 

[Nick Rose]

I guess SPS are tougher then we think.

 

[Suohhen]

I guess SPS are tougher then we think.

Well I guess it is like they say stability promotes success not salinity.

 

[Nick Rose]

So I recently did 2 ICP test, Triton and ATI. Since ATI test salinity I was curious to see their reading on salinity. The reading came out at 32.9psu/ppt. This actually closely matches the Hanna checker which was reading 32.2ppt. So ATI is 32.9, Hanna 32.2, Refractometer 35 and hydrometer is 1.026 or 34.5ppt.

 

[Nick Rose]

@Randy Holmes-Farley

So the salinity debate is back on. I sent ATI-ICP test out for both of my tanks. The salinity came back at 33ppt while Hanna 32.2, Refractometer 35 and Tropic marine high precision hydrometer is 1.026 or 34.5ppt. I have attached my results of both tanks. Also I emailed ATI about this and they sent a photo of them testing the salinity. Would any of the elements indicate that the conductivity devices are the ones showing the true salinity unlike the refractometer.


This is response from ATI:

“Dear Nick Rose,

natural seawater has a specific composition. Please check the following info:

SALINITY AND THE INFLUENCE ON THE CONCENTRATION OF SEAWATER ELEMENTS (INCLUDING THE CALCULATION TOOL) » ATI-Aquaristik

The data of the ICP analyzers are used to calculate two different kind of salinities.
1. The overall salinity is listed in the report and this is the salinity you are also able to test at home.
2. The NaCl based salinity gives us the opportunity to check if the composition of your water is almost natural or not.

The calculated reference values are based on the NaCl salinity. The element concentrations of your sample (values) are compared with the reference values- The differences are listed in the report list as well.
If you have a closer lock at your results, you will see that the concentrations of magnesium, calcium, chloride and some others are higher than expected for the determined NaCl based salinity. Others like sodium are lower than expected.

I am not sure how this affects the determination of the salinity with an refractometer. For the conductivity meter it is not a problem.


Mit freundlichen Grüßen / With best regards


Dr. Ben Funk
Laborleitung“

//lab.atiaquaristik.com/share/e16a0e89c5ee321c01b2
//lab.atiaquaristik.com/share/626576717333e0129886

@Doug

 

[Randy Holmes-Farley]

Ions being somewhat off are not a significant issue for the types of salinity determination we use.

What refractometer are you using and exactly what was it calibrated with (brand). Same question for Hanna: what was it calibrated with?

Did both correctly read the standard after calibration?

For example, my 35 ppt seawater equivalent DIY for calibrating a refractometer is NOT suitable for calibrating other devices (like a conductivity meter) and so one cannot assume that all standard can be used with all device types.

You might next time bring the standard(s) to tank temp to eliminate the temp correction as a factor.

 

[Nick Rose]

Ions being somewhat off are not a significant issue for the types of salinity determination we use.

What refractometer are you using and exactly what was it calibrated with (brand). Same question for Hanna: what was it calibrated with?

Did both correctly read the standard after calibration?

For example, my 35 ppt seawater equivalent DIY for calibrating a refractometer is NOT suitable for calibrating other devices (like a conductivity meter) and so one cannot assume that all standard can be used with all device types.

You might next time bring the standard(s) to tank temp to eliminate the temp correction as a factor.

The refractometer is a Opticon Series FG100sa. I also tested with other refractometers in April and it’s the same results.

All fluid bottles and refractometer were floated in ziplock bags in tank sump. The first two fluids (Brightwell & Continuum) both came to 35ppt. So I tested the next bottle (AccuBrate) which came to 34ppt.

Hanna and it’s calibration packet were also floated in tank water.

I then tested new salt water and these were the results:
Refractometer - 35ppt
Hanna - 32.2ppt
Tropic marine high precision
hydrometer - 1.026 or 34.5ppt

 

[Suohhen]

So your seeing a -.7 ppt difference between api and hanna, 1.5 hydro, and 2 refract. Not the most significant variance especially considering the difficulty of accurately reading a refractometer super accurately with the scale being so small. Also people tend to see what they are used to seeing so since 35ppt is the norm it wouldn't be surprising if at the lfs it was slightly below and they read it as 35. And I notice sometimes when I haven't calibrated my refract for a while it doesn't want to hold the new calibration well until I do it a few times.
Also there has been some time between testing and salinity can drift and depending on the method of top off it can vary somewhat.
So I would recommend you follow Randy's recipe for diy calibration fluid and very carefully calibrate, check and recheck. Also you can add up all the numbers from your icp test and see what number you get from that.