Red Sea Refractometer frustration

Velcro · Jul 27, 2017

I just want to leave my feedback on this thing. I've been using it for months and I have to say that it's just pretty bad altogether.

This thing has to be calibrated every 5 minutes during use. It absolutely does not hold calibration at all. This seems to be the norm for it based on various reviews around the forums. Definitely regret purchasing considering how much more it was than cheaper units that work much better.

Js.Aqua.Project · Jul 27, 2017

Do you mind elaborating? I've been using one for years and and have never had issues. Granted when I get an odd ball number I will double check against RO and recalibrate as needed. But this normally only occurs once or twice every couple of weeks.

Velcro · Jul 27, 2017

Js.Aqua.Project said:
Do you mind elaborating? I've been using one for years and and have never had issues. Granted when I get an odd ball number I will double check against RO and recalibrate as needed. But this normally only occurs once or twice every couple of weeks.

To start, I use temperature matched 35 ppt refractometer calibration solution. I know they say use RODI but that's just stupid and anyone that knows how instrument calibration works would agree. I obviously tried to use RODI and then double check against 35ppt seawater reference solution and it was 2-3ppt off when calibrating with RODI.

My elaboration is that if you calibrate it with solution, walk away from it and come back and recheck calibration it's usually 3ppt off. I don't know if it is just extremely sensitive to room temperature or what the deal is but it just goes out of calibration very fast.

tatansaurus · Jul 27, 2017

I use the same as velcro, temperature matched 35ppt... is much closer to your salinity and withthe RODI you are calibrating to 0 which is much farther than 35ppt to your gravity.
I try to measure when I do at the same time in the same light i use my natural light around 4 pm... also make sure you have no air bubbles on your latch

SPR1968 · Jul 28, 2017

I have one and you just need to calibrate it before each use otherwise you'll get incorrect readings especially with changes to ambient temperature. I spoke with Red Sea about it a while ago. Well after making constant changes to correct my salinity which was actually ok!

I just drop some RODI water on it to calibrate it before using and it only takes a few seconds. I've also got the calibration fluid but they are the same so I mainly use RODI.

chipmunkofdoom2 · Jul 28, 2017

SPR1968 said:
I just drop some RODI water on it to calibrate it before using and it only takes a few seconds. I've also got the calibration fluid but they are the same so I mainly use RODI.

Calibrating with RO/DI is not the same as calibrating with a 35ppt refractive index standard. It's only the same if your refractometer is perfect and has perfect internal calibration. Randy's article on salinity measurement covers the various reasons why. Figure 17 in particular describe a situation like you mention, calibrating with 0 ppt water (freshwater), and the error that results at 35ppt. If you wanted to test this, you could do so by calibrating with freshwater, then read a 35ppt refractive index standard. If the reading is exactly 35ppt, then you have a perfect refractometer. If not, you're one of many reefers who have an imperfect refractometer, and you need to calibrate with a 35ppt standard.

I think this is why this is such a debated topic. Some people have perfect refractometers. They can calibrate with 0 ppt and it will read perfectly at 35ppt. Others, however, do not. Yet, even if your refractometer is not perfect, calibrating with freshwater will likely be close enough (even though it might be off by a ppt or two). The refractometer will be consistent, so your salinity will be consistently a ppt or two off, which likely won't be a big deal. Still, regardless of how accurate your refractometer is, you will always measure accurately at 35 ppt salinity if you use a 35 ppt salinity standard. You will not always measure accurately at 35 ppt salinity if you calibrate with freshwater. To me, this is reason enough to only calibrate with a 35ppt standard.

When a bottle of salinity standard is a few dollars (or you can make your own in a few minutes), it just doesn't make sense to me to calibrate with anything else. I just can't justify salinity being "close enough" when we spend so much on our tanks.

SPR1968 · Jul 28, 2017

chipmunkofdoom2 said:
Calibrating with RO/DI is not the same as calibrating with a 35ppt refractive index standard. It's only the same if your refractometer is perfect and has perfect internal calibration. Randy's article on salinity measurement covers the various reasons why. Figure 17 in particular describe a situation like you mention, calibrating with 0 ppt water (freshwater), and the error that results at 35ppt. If you wanted to test this, you could do so by calibrating with freshwater, then read a 35ppt refractive index standard. If the reading is exactly 35ppt, then you have a perfect refractometer. If not, you're one of many reefers who have an imperfect refractometer, and you need to calibrate with a 35ppt standard.

I think this is why this is such a debated topic. Some people have perfect refractometers. They can calibrate with 0 ppt and it will read perfectly at 35ppt. Others, however, do not. Yet, even if your refractometer is not perfect, calibrating with freshwater will likely be close enough (even though it might be off by a ppt or two). The refractometer will be consistent, so your salinity will be consistently a ppt or two off, which likely won't be a big deal. Still, regardless of how accurate your refractometer is, you will always measure accurately at 35 ppt salinity if you use a 35 ppt salinity standard. You will not always measure accurately at 35 ppt salinity if you calibrate with freshwater. To me, this is reason enough to only calibrate with a 35ppt standard.

When a bottle of salinity standard is a few dollars (or you can make your own in a few minutes), it just doesn't make sense to me to calibrate with anything else. I just can't justify salinity being "close enough" when we spend so much on our tanks.

Yep I wouldn't disagree at all, but I'm just saying that certainly with my Red Sea Refractometer, which is the one we are specifically talking about here, wether I use RODI or 35ppt it's exactly the same calibration level if done within a few seconds/minutes of each reading. I have both liquids.

The following if relevant is from their web site but I don't claim to understand it all by any means:

Main features of Red Sea’s Seawater Refractometer include:

Directly reads the absolute salinity of seawater at 25°C/77 0F ( No need for seawater or temperature compensation factors)
Specifically designed for the ionic content of seawater (NSW) for more accurate salinity measurement (industry standard refractometers are calibrated for salt brine ).
Calibrated for seawater (NSW) at 25oC/77oF, the normal temperature range for reef aquariums
(most standard refractometers are calibrated at 15oC/59oF ).
Easier to read, higher resolution display, focussed to the relevant range for reef aquariums of up to 40ppt
Includes Integrated Automatic Temperature Compensation (ATC) for accurate measurement at standard ambient temperature.

Water Dog · Jul 28, 2017

I got rid of my Red Sea refractometer... hated it. I would calibrate it, take a measurement of tank water, then calibrate it again just to verify. By the 3rd step in my process, it would be off again. The calibration literally drifted in a span of 2 minutes!

Now I use my Milwaukee digital. No more fussing.

HolisticBear · Jul 28, 2017

Velcro said:
This thing has to be calibrated every 5 minutes during use. It absolutely does not hold calibration at all. This seems to be the norm for it based on various reviews around the forums. Definitely regret purchasing considering how much more it was than cheaper units that work much better.

I had the same experience as you and read similar reports, I ordered the BRS one as result and have been very happy with it. Highly recommend.

Velcro · Jul 28, 2017

MrMichael said:
I had the same experience as you and read similar reports, I ordered the BRS one as result and have been very happy with it. Highly recommend.

Mine gets delivered Monday

chipmunkofdoom2 · Jul 28, 2017

SPR1968 said:
Yep I wouldn't disagree at all, but I'm just saying that certainly with my Red Sea Refractometer, which is the one we are specifically talking about here, wether I use RODI or 35ppt it's exactly the same calibration level if done within a few seconds/minutes of each reading. I have both liquids.

That was my point, they are only the same if your refractometer has perfect calibration. Your refractometer appears to have good internal calibration, so for you RO/DI and 35ppt calibration fluid are the same. @Velcro follows the same procedure you do and he gets different results. So for him and many others, freshwater and calibration fluid are not the same.

If you want accurate results at 35ppt, the only way to guarantee that is to calibrate at 35ppt. RO/DI will likely produce consistent results that are "good enough." But I'm not looking for "good enough." Calibration fluid will always produce accurate results every time for every refractometer. Freshwater will not.

Karl M · Oct 31, 2017

Water Dog said:
I got rid of my Red Sea refractometer... hated it. I would calibrate it, take a measurement of tank water, then calibrate it again just to verify. By the 3rd step in my process, it would be off again. The calibration literally drifted in a span of 2 minutes!

Now I use my Milwaukee digital. No more fussing.

I am having the same experience with the Red Sea, it is very frustrating. At least I am not alone with this issue, Calibrated it with 35ppt solution, clean and dry, immediately check agian with same solution it will be off by 2ppt the longer I wait the greater the difference. when cal.to 35ppt then checking RODI is low by 3ppt.

DSC reef · Oct 31, 2017

I love my red sea refractometer. Easy to read too. I've always calibrated with solution before every test so it's normal to me. I can see it being troublesome if your used to having a refractometer you don't need to calibrate often. I will say though mine holds the calibration, maybe you got a bad one.

Karl M · Oct 31, 2017

I am going to do some more testing before I throw in the towel. Did a little more investigating, the only thing that I am not sure about is that I may be holding the metal part there by raising the temperature and Skewing the results ? Then comes the phone call.

Lionfish hunter · May 23, 2021

chipmunkofdoom2 said:
Calibrating with RO/DI is not the same as calibrating with a 35ppt refractive index standard. It's only the same if your refractometer is perfect and has perfect internal calibration. Randy's article on salinity measurement covers the various reasons why. Figure 17 in particular describe a situation like you mention, calibrating with 0 ppt water (freshwater), and the error that results at 35ppt. If you wanted to test this, you could do so by calibrating with freshwater, then read a 35ppt refractive index standard. If the reading is exactly 35ppt, then you have a perfect refractometer. If not, you're one of many reefers who have an imperfect refractometer, and you need to calibrate with a 35ppt standard.

I think this is why this is such a debated topic. Some people have perfect refractometers. They can calibrate with 0 ppt and it will read perfectly at 35ppt. Others, however, do not. Yet, even if your refractometer is not perfect, calibrating with freshwater will likely be close enough (even though it might be off by a ppt or two). The refractometer will be consistent, so your salinity will be consistently a ppt or two off, which likely won't be a big deal. Still, regardless of how accurate your refractometer is, you will always measure accurately at 35 ppt salinity if you use a 35 ppt salinity standard. You will not always measure accurately at 35 ppt salinity if you calibrate with freshwater. To me, this is reason enough to only calibrate with a 35ppt standard.

When a bottle of salinity standard is a few dollars (or you can make your own in a few minutes), it just doesn't make sense to me to calibrate with anything else. I just can't justify salinity being "close enough" when we spend so much on our tanks.

I would be interested in knowing if these solutions are actually seawater 35ppt or just nacl 35ppt. There is absolutely a difference. The calcium, magnesium, etc in sea water will give a different reading. I can‘t really tell for sure on any of the solutions if this is accounted for, so until somebody can confirm this for me, I feel like I have to use the ro/di water that red sea tells you to use. Most refractometers are not sea water refractometers, and most solutions are not either. There is a difference.

chipmunkofdoom2 · May 25, 2021

Lionfish hunter said:
I would be interested in knowing if these solutions are actually seawater 35ppt or just nacl 35ppt. There is absolutely a difference. The calcium, magnesium, etc in sea water will give a different reading. I can‘t really tell for sure on any of the solutions if this is accounted for, so until somebody can confirm this for me, I feel like I have to use the ro/di water that red sea tells you to use. Most refractometers are not sea water refractometers, and most solutions are not either. There is a difference.

This is covered in the article. There are different recipes for each measurement technique because each type of device needs different concentrations of NaCl to approximate seawater. The refractive index solution is 3.65% NaCl by weight, the specific gravity solution is 3.714% NaCl by weight, and the conductivity standard is 3.29% NaCl by weight.