Help pls - Refractometers conflicting - Red Sea vs Other

[Starvin Marvin]

Hey!

Refractometers. When you only have 1, and you don't even know that it might not be calibrated or even designed for Seawater - that ignorance truly is bliss.

I used such a Refractometer for over 2 years with no issues that I perceived to be from inaccurate salt content. But now thinking back - who knows?

I've tried to educate myself by reading numerous posts and articles, including the huge detailed article on Reef Keeping by Randy Holmes-Farley.

I made the DIY Salt Standard according to his Recipe.

I calibrated to Distilled Water. Then I read a tank-temperature (26.5'C) DIY Salt Standard on both my "Random Refractometer" and my "Red Sea Seawater Refractometer".

I adjusted a little bit - not much - so they both read 35 ppt.

Then I tested my Reef Tank water which the GHL Probe is saying is 52 ms conductivity.
(Probe calibrated with 53 ms solution about a week ago)

This is what I'm getting on the 2 refractometers:

It's really puzzling. 5 ppt out? Seems excessive.

I went back and checked against the DIY Salt Solution (18 grams of salt dissolved in 482 grams of distilled water, then placed in mason jar and floated in my sump until it was up to temperature) and this is what I am getting. It's close to 35 ppt each, not perfect any more but not sure why. But close, as +/- 1 ppt would not bother me much.

Then I checked Distilled Water again and this is where I'm sitting. Again - close to 0 each, not perfect but I wouldn't expect to be after the minute adjustments I made at the 35 ppt calibration.

So basically I'm stumped.

My refractometers are within a 1 ppt margin of error of each other with both Distilled Water and with DIY 35 ppt Standard, yet are 5 ppt off on Reef Tank water.


I can't see how this would be due to Red Sea's advertised "built for Seawater" claim.

Even if my original Refractometer was made for straight Brine solution (I have no idea) it should only be 1.8 ppt high from what I have read... right?

I would honesty expect, with the results shown above in the images and the assumption that my Other Refractometer is made for Brine - that the Red Sea would show 33.2 ppt at the lowest.

Or should I have calibrated my Red Sea to read 1.8 ppt higher than 35 with the DIY Standard Solution?

Appreciate in advance, any help you can provide as to what my best next move is to have instruments I'm using correctly and are providing me good numbers.


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[Redfish1980]

I'm not sure my answer will be any help but I'll give it anyway. After fighting a similar fight with several tools that gave different readings and killing a bunch of coral trusting one over another I was given advice from a scientist. He said the only way to make sure the test can not be wrong is to use a tool that can not calibrated. He suggested a glass floating hydrometer used inside a test cylinder.
You fill the cylinder with water and float the hydrometer to get an exact reading every time. Its what Ive seen used at several aquaculture facilities. As long as you dry the hydrometer off when you're done it never wears out and is always accurate. Hope this helps.

 

[Starvin Marvin]

Thanks, it does help and I will get one to use as a cross check.

This morning I tried again but this time I left the instruments in the warmest room of the house overnight and then I waited a full 60 seconds after squishing the water under the viewing plates.

They are somehow reading within 1 ppt, even closer maybe, of each other and definitely within 2 ppt of the conductivity meter.

So now I am beginning to wonder if the Red Sea is extremely sensitive to temperature changes within the Unit itself prior to adding the water...


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[bertoni]

I am not sure what's up with those refractometers, but the scales are for different reference temperatures. I'm not sure how different the scale for 20 C would be, but you need to be using the 25 C scale for reasonable accuracy away from the calibration point. Also, the temperature compensation, if there is any, might not be working.

 

[outssider]

So now I am beginning to wonder if the Red Sea is extremely sensitive to temperature changes within the Unit itself prior to adding the water...


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My refractometer is extremely sensitive to temperature changes despite being labeled as "ATC"....

I take the refractometer out hours before use and set it in the area it's to be used. I calibrate it just before I use it. Just a couple degree temperature difference in the unit itself can make a difference.

 

[Reefer40b]

Now this could be a completely dumb comment but is it possible you took a water sample right near where your ATO dumps into the tank/sump and just happened to be running while you were taking the sample?

Or is this very repeatable with the tank water always being 5 out?

 

[ericarenee]

My Solution to a NEWLY Made problem..

5
They just work.. Easy to read and 110% accurate in any Room temp. No Calibration Required....

I wasted money buying refract-o-wrong-meter..

My two cents . Sometimes the simplest tools are the best...

 

[Starvin Marvin]

...is it possible you took a water sample right near where your ATO dumps into the tank/sump and just happened to be running while you were taking the sample?

On this system - no because it's a Red Sea Reefer and the ATO is limited to a few drops per second. Good thought though!




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[Starvin Marvin]

I wasted money buying refract-o-wrong-meter..

My two cents . Sometimes the simplest tools are the best...

I'm definitely going to get some of those. Love the simplicity and inherent accuracy. Never heard of them until the replies to this Thread!



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[ericarenee]

I'm definitely going to get some of those. Love the simplicity and inherent accuracy. Never heard of them until the replies to this Thread!



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Just google lab grade hydrometer its what we used (I still do) before refractometers where pushed onto everyone to get them to spend more money..

 

[bertoni]

Hydrometers can be accurate, but they are temperature sensitive and I'd calibrate before trusting them, although a good grade should be okay. You would want want designed to read saltwater referenced to 25 C, and probably one for use at 25 C, as well.

 

[Starvin Marvin]

I have contacted Cole-Parmer and asked for some technical recommendation on an appropriate one with the correct temperature and SG range.

Once I've settled on one, I'll post back what it is. Great advice above and thank you


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[outssider]

I have contacted Cole-Parmer and asked for some technical recommendation on an appropriate one with the correct temperature and SG range.

Once I've settled on one, I'll post back what it is. Great advice above and thank you


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I'll bet a good lab grade one wont be cheap !....And don't you need a beaker as well.....

seems kind of messy/dippy

 

[ericarenee]

I'll bet a good lab grade one wont be cheap !....And don't you need a beaker as well.....

seems kind of messy/dippy

They run in 60.00 range.. I paid less for mine if i remember right its gotta be over 20 years old.

 

[bertoni]

I'll be interested in seeing which model they might have.

 

[jcjrogers]

I'm a little confused. I've never had a lab grade hydrometer but have used hobby grade hydrometers both with reef tanks and wine making... they are dependent on temperature (have to be temperature corrected) and aren't that accurate. True, they don't have some of the issues that swing-arm hydrometers have, but they have issues and can be difficult to read.

 

[Redfish1980]

I'll bet a good lab grade one wont be cheap !....And don't you need a beaker as well.....

seems kind of messy/dippy

I bought a lab grade one with a beaker from a LFS in Tamps for $25. Its really easy to use. I dip out enough water to float the hydrometer in the beaker, let it settle for a few seconds and read the salinity. The water can be poured right back into the tank. There is nothing to go wrong other than breaking the thin glass part of the hygrometer.

 

[GimpyFin]

The Milwaukee digital refractometers are also excellent. They don't use a solution and calibrate with just ro/di or distilled. They're accurate, easy to use, and stay calibrated so you're not constantly fussing with them.

 

[tkeracer619]

Red Sea refractometers aren't good at all IMO

 

[Starvin Marvin]

The Milwaukee digital refractometers are also excellent. They don't use a solution and calibrate with just ro/di or distilled. They're accurate, easy to use, and stay calibrated so you're not constantly fussing with them.

I was actually looking for first-hand testimonies of this unit. Seems like you have been impressed with it. Could you clarify whether you have ever checked it against a reference solution or actual sea water?

Or could it be just giving the "impression" that it's accurate because it's "consistent", yet maybe consistently wrong by a couple of ppt?

The data sheet for the product indicates that the "resolution" is 0.001, and the "accuracy" is 0.002. It unfortunately does not say if that is SG, PSU, or ppt. If it was ppt, that would be unbelievably good, likely impossible. If it is SG, it's nowhere near acceptable...

I need to be able to distinguish between 1.024 and 1.026 with accuracy, that tolerance would simply be too wide.



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