True seawater refractometer?

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Does anyone know if those cheap amazon refractometers (for $20) that say they measure seawater salinity actually do so and are not brine refractometers?


I just need a new one and don't feel like paying $80, and I have no way to tell if a company is lying about it or not.
 
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Tidal Gardens
Randy Holmes-Farley said:
Do you have a link to it?
Click to expand...

I'm on my phone at the moment so this is a screenshot of one but I can post a link in a bit.
Screenshot_20230315-172315~2.png
 
I may just buy the digital Hanna stick one but tests like that make me anxious as I have no clue how often they drift off of the calibrated number.
 
I have an old marine depot one I purchased in 2009. It’s been well used and then in storage for 12 years. I checked it’s calibration against a LFS that uses a Milwaukee salinity checker and it was still spot on. I was surprised but apparently a redractometer will hold calibration of you take care of it.
 
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Avast
Spare time said:
I may just buy the digital Hanna stick one but tests like that make me anxious as I have no clue how often they drift off of the calibrated number.
Click to expand...
I have the Hanna HI98319 and it is not accurate compared to 3 refractometers. Its useable because it doesn't drift but it is 0.02 low so I just compensate
 
TokenReefer said:
Correct me if I'm wrong but if you're using a 35 ppt standard I don't see a difference between that one and the more expensive ones... What am I missing?
Click to expand...

Well, that's like saying if my cheap one is accurate, what is better about a more expensive one. Lifetime? Frequency of recalibration? Ease of use?
 
Nutramar Foods
I'm suspicious that the refractometer pictured above is not really a true seawater refractometer.

The two different scales do line up for a sodium chloride solutiona nd do not line up for a seawater solution,.

hence, IMO, it is a brine refractometer and should be calibrated with a 35 ppt stadnard and NOT RO/DI or any other fresh water source.
 
Last edited:
Spare time said:
I may just buy the digital Hanna stick one but tests like that make me anxious as I have no clue how often they drift off of the calibrated number.
Click to expand...
you will not be upset about your purchase. It comes with calibration fluid. If you rinse it in RO after every use it will only need calibrated monthly.

I am not sure if this is a bad idea or not, but I just grabbed some of my 1.026 tank water and keep it in a jug and use it as calibration fluid. ICP test came back matching exactly what I had been under the impression of. 100% recommend. Don't waste your time with the refactometers they will get rusty and a royal PITA
 
ilikefish69 said:
you will not be upset about your purchase. It comes with calibration fluid. If you rinse it in RO after every use it will only need calibrated monthly.

I am not sure if this is a bad idea or not, but I just grabbed some of my 1.026 tank water and keep it in a jug and use it as calibration fluid. ICP test came back matching exactly what I had been under the impression of. 100% recommend. Don't waste your time with the refactometers they will get rusty and a royal PITA
Click to expand...

What salinity is the calibration fluid?
 
Nutramar Foods
Mine was bought when they first came out in uk my LFS it wasn’t that cheap at the time carnt remember how much but still in use today . Still very accurate. Make is by TMC my calibration is water with a screw you turn to 0 and that’s it
223BF9D2-3EA8-423F-B761-B099C05599A1.jpeg
E36B986F-5586-4F54-8778-9202883FC7EB.jpeg
 
ilikefish69 said:
the Hanna came with 35 PPT , I just have about a gallon of my tank water that was ICP tested as the back up when I run out of the Hanna packets. I believe there were 6 included
Click to expand...

Sorry, I thought you were talking about the refractometer of the OP when you said it came with fluid. That Hanna fluid should be fine for the Hanna if made properly.
 
Top Shelf Aquatics
Randy Holmes-Farley said:
I'm suspicious that the refractometer pictured above is not really a true seawater refractometer.

The two different scales do line up for a sodium chloride solutiona nd do not line up for a seawater solution,.

hence, IMO, it is a brine refractometer and should be calibrated with a 35 ppt stadnard and NOT RO/DI or any other fresh water source.
Click to expand...

So it's really only a tiny bit off when calibrated to 35ppt right? At least that's what I remember from your article
 
What are the critical or safe boundaries regrading salinity in a reef aquarium? and how does this effect ones consideration with regards general accuracy when purchasing test equipment. ?

I was of the understanding that a range of between 29 ppt to 39 ppt was within a safe boundary. ?

Just for sake of interest, I like to have a robust piece of test equipment if possible. I liked the DD refractometer (around £45) and for my shop I used the Hanna HI 933000 conductivity meter (around £600). I also had a range of calibration samples.

Hobby kit tends to get thrown around so I advise a robust bit of kit that is within budget. Automatic temp compensation and a clear reading scale may also help.

The TMC refractometer mentioned earlier I had a number of these returned to my store broken, I stopped selling them.

I still don't understand why some people calibrate their refractometer at 0. I always use 35ppt. Can you shed some light on this @Randy Holmes-Farley
 

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