Refractometer

[denhay14]

I think I need to get a refractometer, but I'm not sure which is a good one. I'm looking on ebay and this one seems pretty good just not sure. It's a RHS-10ATC portable salinity refractometer

[Ninong]

I think I need to get a refractometer, but I'm not sure which is a good one. I'm looking on ebay and this one seems pretty good just not sure. It's a RHS-10ATC portable salinity refractometer

Yes, that's the one you want. They usually sell for about $44 at most online vendors, so I'm a little surprised to see them for only $24 on eBay but that appears to be the same one. The important thing is that it should say "10ATC," which it does. That appears to be identical to the ones that are $44-$45 at most online vendors.

Good luck!



P.S. -- Remember, this is a NaCl refractometer, not a seawater refractometer. All of the hobby refractometers are NaCl refractometers. True seawater refractometers just aren't available in this price range. This is NOT a problem.

There are two ways to adjust for the fact that it is not a true seawater refractometer: 1) Recalibrate it using a known 35 PSU (35 ppt) calibration fluid, or 2) simply adjust your reading. Option #2 is perfectly acceptable.

For starters, ignore the specific gravity side of the scale. Now that you have a refractometer there is absolutely no reason to report salinity as anything other than salinity. Specific gravity is only a substitute for salinity. What I always did was to shoot for a reading of 36 ppt on the salinity scale, knowing that that meant that my true salinity was between 34-35 ppt. To be exact, it was 34.3 ppt. That's because of the adjustment that you have to make when calibrating this NaCl refractometer with freshwater (distilled water of R.O./D.I. water) so that the freshwater equals zero. It will come from the factory already calibrated. You should check it with freshwater just to make sure that freshwater equals zero.

You could always purchase a known solution of 35 ppt salinity and calibrate it so that that solution reads 35 ppt on the scale. In which case, freshwater will no longer read zero. This is really completely unnecessary. It's perfectly acceptable to calibrate it with freshwater reading zero and then make the adjustment in your head.

If you do not make this adjustment in your head and choose to simply go with a reading of 35 ppt on the salinity scale of the refractometer, then your true salinity will be 33.3 ppt.

[denhay14]

Alright just to make sure I understand. All I have to do it stick it in some distilled water and make sure it reads zero. If it does then i'm good to check the salinity of my tank. That should read somewhere between 34-35 ppt. If it does then im good.

[Ninong]

Alright just to make sure I understand. All I have to do it stick it in some distilled water...

No! You don't stick it in the water. :eek3:

You place a couple of drops of water on the glass plate and then close the lid glass. You need just enough water so that after the lid is lowered, there is a thin film of water between the two plates of glass. Then you hold the refractometer up to light so that the light passes through the two plates of glass and the thin film of water that is trapped between them. There will be instructions that come with it. Just read the instructions and then post again if you still have questions.

...and make sure it reads zero.

It will read zero. I would be shocked if it doesn't.

If it does then i'm good to check the salinity of my tank. That should read somewhere between 34-35 ppt. If it does then im good.

No, you don't want it to read between 34-35 ppt on the salinity scale. You want it to read 36 ppt or even between 36 and 37 ppt. If it reads 36 ppt, then that means that your salinity is actually 34.3 ppt. Remember, you have to make the adjustment in your head. If it reads 35 ppt on the salinity scale, that means your salinity is actually 33.3 ppt, which is a little low.

Your goal is to keep the salinity between 34-35 ppt and to do that you need the refractometer to read 36 ppt.

Good luck!

[denhay14]

So you just subtract 1.7 from the actual number I read.

[Ninong]

So you just subtract 1.7 from the actual number I read.

Yes. If you read 36 ppt on the salinity scale of the refractometer, you actually have 34.3 ppt salinity. That's assuming it's a NaCl (sodium chloride) refractometer calibrated so that distilled water equals zero, which is what you are getting. That's what everybody has except that most of them don't know about this adjustment to the reading. They think that if it reads 35 ppt, that means they have 35 ppt salinity. They don't. They have 33.3 ppt salinity, they just don't know it.

If you want to maintain 35 ppt salinity instead of 34.3 ppt, then you should shoot for a reading of 36.5 ppt on the salinity scale of the refractometer. The 1.7 adjustment difference changes slightly at different readings. As long as you read 36 ppt on the refractometer's salinity scale, or just barely above it, then you're in great shape.

Go for it.



P.S. -- That's a very good price!

P.P.S. -- Dr. Randy Holmes-Farley discusses Refractometers and Salinity Measurement. I do not want you to read that article because it will just confuse you. He's talking about stuff that you don't need. The only thing I will quote from that article for you is the followsing:

...a perfectly made sodium chloride refractometer necessarily has a different relationship between refractive index and salinity than does seawater. ...If you have this type of refractometer, and it was perfectly made and calibrated in freshwater, it will ALWAYS read seawater to be higher in salinity than it actually is (misreporting an actual 33.3 ppt to be 35 ppt).

So now you don't have to read Randy's article because I copied the only part I want you to read right now, especially at your age. Most of the article deals with the various types of refractometers and how to calibrate them if they need calibration. It's an excruciatingly technical acticle that will just give you a headache.

[denhay14]

Haha thanks I learn a lot here but some stuff is really confusing and don't think I will get for a while. Like lighting i'm soooo confused, and building stuff which doesn't really matter but still I dont get lol.

[cdearing]

The refractometer that is being sold on EBay uses ambient light so no batteries. Are they just as easy to read as the ones with an inner light?

[Nemo Keeper]

I have been looking around for one of these. This is a GREAT price. I just made my purchase!!!!

[Ninong]

The refractometer that is being sold on EBay uses ambient light so no batteries. Are they just as easy to read as the ones with an inner light?

Yes, they are quite easy to read with bright daylight from any open window -- not direct sunlight, just bright light from near the window. It's okay to use sunlight, just not necessary.

That's the same way you should read the color changes when evaluating test results. Just as you hold the test vials up to a bright window, you would hold the refractometer in front of the window so that it receives bright daylight. (P.S. -- Maybe that's a bad comparison because color changes in test fluids are meant to be read using bright ambient light, not sunlight or artificial light. A refractometer can be read using sunlight but bright ambient light next to an open window is more than adequate to get an accurate reading.)

Whenever I wanted to use my refractometer at night, I would hold it near the rim of the aquarium beneath the light fixture, which was mounted over the center of the tank and 11" above the water's surface. However, I believe daylight is better but any difference would be insignificant anyway. (P.S. -- On cloudy days, if I couldn't see the scale well enough indoors, I would walk outside and take the reading there. Probably more than 90% of hobbyists use this type of refractometer. Nobody pays extra for the battery-operated ones.)

[denhay14]

No I was talking about lighting for tanks in general. Sorry that I didn't specify. Just like Metal Halides or VHO HO all that kind of stuff I don't get the differences and which lights go with which kind of aquariums.

[Ninong]

No I was talking about lighting for tanks in general. Sorry that I didn't specify. Just like Metal Halides or VHO HO all that kind of stuff I don't get the differences and which lights go with which kind of aquariums.

Cynthia was asking if the refractometers like the ones advertised on eBay are just as good as the ones with battery-operated lighting and my response was to her telling her that they are fine. You don't need lighted refractometers. Regular refractometers that you hold up to the light are fine.

[denhay14]

oh alright my bad.

[Ninong]

No I was talking about lighting for tanks in general. Sorry that I didn't specify. Just like Metal Halides or VHO HO all that kind of stuff I don't get the differences and which lights go with which kind of aquariums.

Dr. Sanjay Joshi has written a series of five articles on The Facts of Light:

Part I: What is Light?
Facts of Light – Part I: What is Light? by Sanjay Joshi - Reefkeeping.com

Part II: Photons
Facts of Light – Part 2: Photons by Sanjay Joshi - Reefkeeping.com

Part III: Making Sense of Light Measures
Facts of Light – Part 3: Making Sense of Light Measures by Sanjay Joshi - Reefkeeping.com

Part IV: Color Temperature
Facts of Light – Part 4: Color Temperature by Sanjay Joshi - Reefkeeping.com

Part V: Everything You Need to Know About Metal Halide Lamps and Ballasts
Facts of Light - Part 5: Everything You Need to Know About Metal Halide Lamps and Ballasts by Sanjay Joshi - Reefkeeping.com

You may be able to understand what he is saying if you put your mind to it. I realize that this is way above where you are in school but if you can get anything out of these articles, you will be way ahead of the game if you ever take physics.

BTW, stop staying up so late on the board on school nights. You were on the board way too late Sunday night.

[Seige]

Yes, that's the one you want. They usually sell for about $44 at most online vendors, so I'm a little surprised to see them for only $24 on eBay but that appears to be the same one. The important thing is that it should say "10ATC," which it does. That appears to be identical to the ones that are $44-$45 at most online vendors.

Good luck!



P.S. -- Remember, this is a NaCl refractometer, not a seawater refractometer. All of the hobby refractometers are NaCl refractometers. True seawater refractometers just aren't available in this price range. This is NOT a problem.

There are two ways to adjust for the fact that it is not a true seawater refractometer: 1) Recalibrate it using a known 35 PSU (35 ppt) calibration fluid, or 2) simply adjust your reading. Option #2 is perfectly acceptable.

For starters, ignore the specific gravity side of the scale. Now that you have a refractometer there is absolutely no reason to report salinity as anything other than salinity. Specific gravity is only a substitute for salinity. What I always did was to shoot for a reading of 36 ppt on the salinity scale, knowing that that meant that my true salinity was between 34-35 ppt. To be exact, it was 34.3 ppt. That's because of the adjustment that you have to make when calibrating this NaCl refractometer with freshwater (distilled water of R.O./D.I. water) so that the freshwater equals zero. It will come from the factory already calibrated. You should check it with freshwater just to make sure that freshwater equals zero.

You could always purchase a known solution of 35 ppt salinity and calibrate it so that that solution reads 35 ppt on the scale. In which case, freshwater will no longer read zero. This is really completely unnecessary. It's perfectly acceptable to calibrate it with freshwater reading zero and then make the adjustment in your head.

If you do not make this adjustment in your head and choose to simply go with a reading of 35 ppt on the salinity scale of the refractometer, then your true salinity will be 33.3 ppt.

Wow Ninong. That made my head hurt...

[Seige]

Haha thanks I learn a lot here but some stuff is really confusing and don't think I will get for a while. Like lighting i'm soooo confused, and building stuff which doesn't really matter but still I dont get lol.

What stuff are you building? I'm going to guess the sump since that's probably the most confusing piece.

If it is sumps, maybe this will help. Scroll down until you see the active demo of the tank and sump.
Melevsreef.com | Acrylic Sumps & Refugiums


.

[Seige]

The important thing is that it should say "10ATC," which it does.

Ug wish I read this earlier. The one I ordered doesn't say 10ATC. What is 10ATC?

Other then being expensive is this one ok?
Salinity Refractometer

[Ninong]

Wow Ninong. That made my head hurt...

Just remember that refractometers are better than hydrometers for checking salinity.

Inexpensive refractometers are available and they are perfectly good for our purposes and much, much better than hydrometers. They do not require battery-operated lights but such instruments are obviously nicer than the ones without lights.

Virtually all of the refractometers that are used by hobbyists are NaCl (sodium chloride) refractometers, not seawater refractometers.

The refractometers should have ATC as part of the model description. ATC stands for automatic temperature compensation. They should have 10 in front of the ATC. This describes the scale. The letters RHS tell you that it is a hand-held instrument without a light.

Salinity should be reported as salinity, not specific gravity. There is really no reason to report salinity as specific gravity. This is totally unnecessary and out of date. The unit of measurement for salinity is PSU (practical salinity units), often abbreviated as S. One PSU = 1 ppt (parts per thousand). For example, S=35, or 35 PSU, or 35 ppt. In scientific literature, you will usually see it written as S=35.

If you insist on reporting salinity as specific gravity, then no one will know whether you bothered to make the necessary adjustment to correct the reading. If you used a refractometer and simply reported what you saw on the scale, then your reading is incorrect if it's a NaCl refractometer, which it almost certainly is. Even if the refractometer is ATC and automatically adjusted for temperature, you still have to correct your reading, whether it's from the salinity scale or the SG scale.

If you're reporting SG from a hydrometer, then you should report the tankwater temperature with it because the salinity at a SG reading in 84-degree Fahrenheit water is not the same as the same SG reading in 75-degree Fahrenheit water.

Specific gravity is only a substitute for salinity. If you know the salinity, why report it as specific gravity. Just report it as salinity but make sure that you have adjusted your reading first. Obviously if you want to go to all the trouble of purchasing a 35 ppt calibration solution to calibrate your refractometer, you will have a more accurate reading. If you're a very good chemist, you could even make your own 35 ppt calibration fluid.

[Ninong]

Ug wish I read this earlier. The one I ordered doesn't say 10ATC.

Yes, it does.

This refractometer is a quality made optical model with automatic temperature compensation.

Other features include:
- Dual scale Salinity and Specific Gravity display
- Measures Specific Gravity from 1.0 to 1.070
- Easy calibration with distilled water
- Adjustable Eyepiece
- Hard plastic carrying case
- Pipette and calibration screwdriver included.

It's an RHS10ATC. They just don't spell it out in plain English like the eBay vendor did.

Other then being expensive is this one ok?
Salinity Refractometer

The Canadian one appears to be the same thing as the one we're talking about for US$24 on eBay. In fact, it appears to be identical. It's just that you paid $58.95 CDN for it.

Description of the US$24 one on eBay:

Product Specs


* Ranges: 0-100 ppt of Salinity and 1.000 to 1.070 Specific Gravity
* Accuracy: +/- 1 ppt / 0.001 Specific Gravity
* Divisions: 1 ppt / 0.001 Specific Gravity
* Automatic Temperature Compensation (ATC)
* Sturdy design made of durable Aluminum, not "carbon" plastic, 3-Year Warranty

P.S. -- Don't feel bad. It usually sells for US$45 at most American online vendors and that equals $57 CDN now that the price of oil has dropped by $100/bbl and the looney has plunged from a high of US$1.08 to US$0.79. It wasn't all that long ago that the looney was only 65 cents American. It skyrocketed when oil hit $147/bbl last July because Canada is a net exporter of oil. The value of the currency of a country that is a net exporter of oil will rise against the value of a country that is a net importer of oil when the price of oil rises.

Real maple syrup is also a lot cheaper now.

[cdearing]

I just ordered one. Thanks for the info.