Homemade refractometer standard

[Cory]

As per Randy's article it calls for Mortons iodized salt. Here in Canada I can only find Sifto brand. It says salt, calcium silicate, sodium thiosulphate, potassium iodide.

Will this work the same as mortons brand?

 

[Oscaror]

I know that feeling of not having all these american products, or corals >_<

 

[Randy Holmes-Farley Verified Community Expert]

The concern is more the bulk density being different, if you measure by volume. If you measure by mass it should be OK.

 

[Cory]

I know that feeling of not having all these american products, or corals >_<

Haha dam that mortons salt! No worries that's why they invented ups.

 

[Cory]

The concern is more the bulk density being different, if you measure by volume. If you measure by mass it should be OK.

I took it to a pharmacy and measured 79.3 grams. I have a kitchen scale and it weighed their salt at 79grams so I know it's accurate, but not precise. No worries about the Ingredients? There was other salt and the Ingredients were just salt. Would that be better?

Also my swing arm hydrometer read 1.026, while the refractometer read 1.025 calibrated with ro/di. Thus I had the suspicion it was off. I went to a fellow reefers house who had calibrated his with a standard. His tank water was 1.028 according to my refractometer and 1.029 according to my swing arm. His tanks are healthy. But my suspicion something was wrong for this. I calibrated using Randy's home made and it reads my tank at 1.024 and his at 1.027. Thus I'm kinda lost about what to believe. My apex conductivity will come in a couple of weeks we'll see what that says.

 

[Skydvr]

Have a link to that article?

 

[Randy Holmes-Farley Verified Community Expert]

I took it to a pharmacy and measured 79.3 grams. I have a kitchen scale and it weighed their salt at 79grams so I know it's accurate, but not precise. No worries about the Ingredients? There was other salt and the Ingredients were just salt. Would that be better?

Also my swing arm hydrometer read 1.026, while the refractometer read 1.025 calibrated with ro/di. Thus I had the suspicion it was off. I went to a fellow reefers house who had calibrated his with a standard. His tank water was 1.028 according to my refractometer and 1.029 according to my swing arm. His tanks are healthy. But my suspicion something was wrong for this. I calibrated using Randy's home made and it reads my tank at 1.024 and his at 1.027. Thus I'm kinda lost about what to believe. My apex conductivity will come in a couple of weeks we'll see what that says.

If you are weighing it, just salt would be better. Maybe not noticeably better, however.

 

[Randy Holmes-Farley Verified Community Expert]

Have a link to that article?

Both of these have it:



Refractometers and Salinity Measurement by Randy Holmes-Farley - Reefkeeping.com


Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

 

[Cory]

Both of these have it:



Refractometers and Salinity Measurement by Randy Holmes-Farley - Reefkeeping.com


Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

Those are the articles. Randy do you think that the swing arm hydrometer is actually reading 3 points low, or is probably accurate?

 

[Skydvr]

Thank you.

 

[Randy Holmes-Farley Verified Community Expert]

Thank you.

:thumb:

Happy Reefing.

 

[Randy Holmes-Farley Verified Community Expert]

Those are the articles. Randy do you think that the swing arm hydrometer is actually reading 3 points low, or is probably accurate?

Swing arms can certainly be substantially in error.

 

[Cory]

Thanks. Can I use the solution I made for the swing arm to see its accuracy? What should it be reading approximately in this refract calibration solution?

 

[Randy Holmes-Farley Verified Community Expert]

Thanks. Can I use the solution I made for the swing arm to see its accuracy? What should it be reading approximately in this refract calibration solution?

YOu either need a slightly different solution, or you need to know that it has a slightly different specific gravity when determined with a hydrometer. The secodn article discusses solutions for hydrometers.

 

[Cory]

YOu either need a slightly different solution, or you need to know that it has a slightly different specific gravity when determined with a hydrometer. The secodn article discusses solutions for hydrometers.

Yes I thought so. But what I'm curious about is what would be the salinity or SG of the refractometer solution in a hydrometer. Is the math possible? This way I wouldn't have to make another one.

 

[Randy Holmes-Farley Verified Community Expert]

It is pretty close,. I'll see what I can figure out.

 

[Cory]

Thanks. So your saying it should be reading about 35ppt on a hydrometer?

 

[joekool]

Randy I have a ATC refractometer from BRS and I have been using it for some time now. I also bought the solution to calibrate with. Problem is if I check pure water it reads below 0. Why is this? Is my solution of 35ppt i calibrate with not right or is something wrong with my refractometer. There is a difference of 5ppt if I calibrate to pure water than solution.

 

[JimWelsh]

Taking the data for refractive index and density of sodium chloride solutions at 20C and various concentrations found here http://chemistry.mdma.ch/hiveboard/rhodium/pdf/chemical-data/prop_aq.pdf and then deriving cubic polynomial equations to describe both, the refractive index of a 3.65% NaCl solution at 20C = 1.33938 and the density = 1.024285. Using a value of 0.998203 for the density of pure water at 20C, this equates to a SG of 1.02613. Seawater at 20C with this SG has a salinity of about 34.4 PPT (rounded to the nearest 0.1 PPT).

EDIT: Responding to Cory, not joekool.

 

[Randy Holmes-Farley Verified Community Expert]

A brine refractometer cannot correctly read both RO/ DI and seawater with the same calibration, so if properly calibrated to read seawater, it will read below 0 in fresh water. I have an article detailing why, but can't link it properly from my phone.

5 ppt sounds too high, however.