Digital Refractometer SG v PPT

richfavinger

richfavinger

Premium Member
:headwally:
Ok, I've been reading up a little. Trying to understand the different measurements using my Milwaukee Digital Refractometer. I am legally blind, so using a standard look-through Refractometer is difficult.

My tank seems to be running a little high. But what measurement to trust?

I've calibrated the Milwaukee Digital Refractometer with Distilled Water per instructions. - My TANK is running 80.5F and I let the sample stand for 1min - press read - I get a temp of 77.5 (according to the Refractometer) and 35ppt / 1.026 SG...

Am I OK?

A different sample I measured in my water change mix barrel was 1.025 but came in at 33ppt (78F) ? - So, what do I go by SG or PPT? I know it's all dependent on temp. The Digital Refractometer has ATC.
 
35ppt / 1.026 is perfect. thats where i keep my tank.
mixing barrel at 1.025 is also good can bump it a hair. is this mix more than 24 hrs old? or is it still new?
 
The mix is more then 24hr, yes (Typically I run for 3-5 days before a water change).

My concern was 1.026 / 35ppt and the tank being 80.5F? (though the Refractometer says 77.5F)
And the mix reading 1.025 and 33ppt... Only 0.001 SG v 3ppt points?
 
sg and ppt are different units of the same measurement. It's like asking whether you should go by degrees C or degrees F.

For actual seawater, 35.0 ppt has a sg of 1.0264 and 33.0 ppt has a sg of 1.0249. So your numbers are in accord.

I cannot tell if it is ATC (automatic temperature control, so I cannot be sure of that issue). Do the instructions say anything about that?

FWIW, I also cannot be sure it is actually properly designed for seawater, so at least once I'd calibrate to 0 ppt (or 0 psu or sg = 1.0000) in fresh water and then test a seawater 35 ppt standard to see if it properly reads 35 or sg = 2.0264. If not, it may be designed like most refractometers for sodium chloride,a dn thereafter you should always calibrate with a 35 ppt seawater standard,.
 
Thanks Randy, I was actually reading your articles last night trying to really understand it.

The meter is the Milwaukee Digital Refractometer MA887, I did try the Aqua Craft Refractometer Calibration Fluid (says 35ppt @ 77F). Though it seems to read a little high. But it is about +/- 1ppt point, and I suppose thats within the meters error.

I will double check my manual, but "ATC" is ON (it's on the LCD).

I have been dosing Magnesium and the tanks salinity was creeping a little high. But I'm receiving my first corals and a new fish today from Divers Den, so I just wanted to be sure of my readings first.
 
We use your refractometer to test injectable sodium chloride soultions, and can tell you it appears it is working properly for you. +1 using 35 ppt reference std as a check for your 0 ppt calibration.
 
Randy Holmes-Farley said:
sg and ppt are different units of the same measurement. It's like asking whether you should go by degrees C or degrees F.

For actual seawater, 35.0 ppt has a sg of 1.0264 and 33.0 ppt has a sg of 1.0249. So your numbers are in accord.

I cannot tell if it is ATC (automatic temperature control, so I cannot be sure of that issue). Do the instructions say anything about that?

FWIW, I also cannot be sure it is actually properly designed for seawater, so at least once I'd calibrate to 0 ppt (or 0 psu or sg = 1.0000) in fresh water and then test a seawater 35 ppt standard to see if it properly reads 35 or sg = 2.0264. If not, it may be designed like most refractometers for sodium chloride,a dn thereafter you should always calibrate with a 35 ppt seawater standard,.
Click to expand...

I have one of these units. It has Automatic Temperature Compensation (guessing that is what you meant?). Per instructions from MI, you calibrate the unit before each use with RODI or distilled water, but once calibrated, can be used between different SW sources, like different reefs or water change setups. User just needs to make sure to clean the lens between each use. You then rinse the eye off with RODI/distilled when you are finished.

Under the skin, the MI Refractometer looks like the same thing as the Hanna Digital Seawater Refractometer.

I have tested mine against my Tropic Marin Precision Hydrometer and it reads the same.
 
Thanks. I'd still like to see if calibration at 0 ppt gives the correct value for a 35 ppt seawater standard. For most refractometers it will not, despite the statements by manufacturers to calibrate at 0 ppt. :)
 
New MA887

New MA887

Sorry to bump an old thread but thought it was appropriate.

Just got an MA887 and calibrated using fresh RO/DI 0 TDS water to 0 as per the instructions. But then when I gave my 35ppt Saybon calibration solution a try on the device it read at 30. Quite a bit off.

But now not sure if it's the calibration solution or the device. Anyone have good or bad things to say on either side? I had been using the solution to calibrate my handheld refractometer so I don't have much else to go on.
 
alienz,
After using the meter for some time now, I must tell you it is very sensitive. I use distilled water in a clear condiments bottle for easy dispensing to "wash" and calibrate the prism between tests.

You must make sure the sensor prism is clean and dry before testing. Start with a 0ppt reading / calibrate... Check it 2 or 3 times if you must... I also often run my tests twice. - I've found that the slightest contamination to really toss a reading badly!

I typically use a paper towel I tear into strips to dab the prism dry between tests. Make sure you get a consistent and ZERO reading before you test any salt samples.
 
Refractometer vs Salinity Meter

Refractometer vs Salinity Meter

I have just recently decided to change over my FOWLR to "reef-ready". In doing so I've been raising my salinity slowly, heading for 1.026. I have a decent refractometer but what I don't have is eyes than can make out the lines with enough confidence.

So I bought a salinity meter, Extech Ec170 (I talked to Extech and this is the meter they suggested). It has two scales, 0-10ppt and 10-70ppt. I also purchased 35ppt solution from Aqua Craft Products.

Upon receiving both I rinsed the probe with RODI and then let it sit in the calibration solution for 30+ min. The probe came up with 37ppt. Following the instructions I recalibrated it to 35ppt. I then used my refractometer on the solution and came up almost exactly 35ppt. So far, so good...

I then tested my tank water with the refractometer and came up around 34ppt. So far, still good...

Then I tested my tank water with the meter and came up with 24.2ppt. So far, so...***?

I redid the tests twice more with the same results. I checked the meter and the refractometer with straight RODI and both came up zero. So unless this is some kind of new math I have to assume there is some kind of difference in the make up of the solution to my ASW and it's conductivity. But that's where my chemistry and physics about hits their limits.

Can somebody help explain what I'm seeing and if there's a better way I should go about making sure my salinity is correct?

Thanks in advance.
 
Did you test the tank with the meter in the water? I would suggest that you take a sample and run the test away from the electrical equipment, if you haven't done that yet.
 
Nope, I used my officially sanctioned sample containment devices, aka new shot glasses rinsed with RODI. The tank is 3 steps from the bar ;-)
 
Hmm, I'm not sure what's happening, but I wouldn't trust the meter just yet. I don't know what the AquaCraft product is, but if it's not intended for conductivity meters, it might not be accurate. I'd try the PinPoint 53 mS solution, personally. 24.2 ppt just seems far too low, though, even with a bad calibration solution.
 
Yeah, I agree to all of the above. Looks like some phone calls to Extech (again...) tomorrow.

What's even more frustrating is that due to extech's complete lack of useful info on any of their salinity meters this is now the 3rd one I'm dealing with. When I call them, even their own tech people have crappy documented info, where they have it all...very disappointing since up until now I've used Extech for the majority of my metering-type needs whenever possible but I believe they've struck out on this project.

Maybe I should just stick with brands that have a presence in the saltwater space, even given their shortfalls.

Anyone know if the Reefkeeper salinity module is accurate and reliable? I've got various pieces of a ReefkeeperLite lying around that I could turn in to a semi-portable metering kit.
 
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