# Refractometer Calibration



## Ctp416 (Nov 23, 2011)

I`ve been calibrating my Refractometer with Ultrapurewater calibration reagent. After zeroing the meter I double check with RO water and still reads 0 ppt.

I just bought Standard Seawater Saline Calibration Solution and calibrated my meter and when I cross checked it with the pure water regent it read .04 instead of .00...

Before I did all this my tank salinity was 1.024 now it reads 1.028! 

Now I don`t know what to trust? Both calibration fluids are made by the same company....

Anyone come across this problem or any suggestions on what to trust?

Thanks for any input.


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## fury165 (Aug 21, 2010)

From what I read, the saline calibration fluid is the way to go.I now use it instead of RO for calibration.


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## Ctp416 (Nov 23, 2011)

I took a sample of my water to a store to test the salinity and turns out that the pure water regent was the accurate solution! The sea water solution is off by .03


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## BIGSHOW (Sep 10, 2011)

Ctp416 said:


> I took a sample of my water to a store to test the salinity and turns out that the pure water regent was the accurate solution! The sea water solution is off by .03


...and what did the store use to test your water? When was it last calibrated and what was used to calibrate there meter?


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## Ctp416 (Nov 23, 2011)

Hydrologist said:


> ...and what did the store use to test your water? When was it last calibrated and what was used to calibrate there meter?


All very good questions..
They used a Refractometer that was also calibrated with pure water.After doing a little research it`s not the first time that salinity solution has known to be off.
I bought a fish and a coral this weekend from different stores and tested both water salinity and both said between 1.024 and 1.025 so i have to believe that my meter is right when calibrated with pure water.


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## altcharacter (Jan 10, 2011)

When we all calibrated our refractometers at the BBQ a few months ago I found out that my water was actually 1.035 rather than 1.026 I was going for due to me calibrting my refractometer with r/o water. Now that I've recalibrated it to match the 1.026 i've found that my tank isn't doing as well...or I don't think it is.

I'm going to purchase some calibration solution soon to make sure it's alright but I do think it's the right thing to do.


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## BIGSHOW (Sep 10, 2011)

Ctp416 said:


> All very good questions..
> They used a Refractometer that was also calibrated with pure water.After doing a little research it`s not the first time that salinity solution has known to be off.
> I bought a fish and a coral this weekend from different stores and tested both water salinity and both said between 1.024 and 1.025 so i have to believe that my meter is right when calibrated with pure water.


Since both stores also use the wrong calibration solution how can you then justify yours being correct? If you don't think you need to calibrate your refractometer using a known saline solution then I suggest you read this article.

http://reefkeeping.com/issues/2006-12/rhf/index.php#11

Just because its a store doing your testing doesn't mean the store is correct.

...From all the reading I have done, most state that if you are calibrating using pure water, you are likely to be off .04 which is exactly what yours was off by.


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## BIGSHOW (Sep 10, 2011)

I don't doubt that some saline calibration solutions can be off, but this is not very common (this percentage of saline solutions being incorrect would probably be the same as the pure water solution). 

If you are really concerned I would be getting two different lab grade saline solutions and measure your refractometer vs. them.

I know for myself, I would rather be calibrating an instrument to the range of values I expect to see.


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## Ctp416 (Nov 23, 2011)

Hydrologist said:


> Since both stores also use the wrong calibration solution how can you then justify yours being correct? If you don't think you need to calibrate your refractometer using a known saline solution then I suggest you read this article.
> 
> http://reefkeeping.com/issues/2006-12/rhf/index.php#11
> 
> ...


Not sure if your aware of this but Sybon Refractometers are sold with Ultrapure water calibration regent.... Both my solutions are made by Sybon so what one should I believe to be correct? I tested water from 3 different tanks and believe that the pure water is giving me a correct reading according to what they tell me their salinity is. For piece of mind i`m going to get the saline solution tested by a few people to make sure the batch isn`t off.


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## altcharacter (Jan 10, 2011)

Just a side note to this thread. When we calibrated our devices at the BBQ everyone calibrated it to the proper 33ppt that the solution is made of. So, since 4 different refractometers are now reading the same solution @ 33ppt they should all read R/O water at the same level, regardless if it's 0 or 4 right?

In our case mine was reading 2-3 and a few others were reading 0 and 5-7. I own a Sybon and think it's still working but this just shows that everyone's tool is going to be different


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## Ctp416 (Nov 23, 2011)

Hydrologist said:


> I don't doubt that some saline calibration solutions can be off, but this is not very common (this percentage of saline solutions being incorrect would probably be the same as the pure water solution).
> 
> If you are really concerned I would be getting two different lab grade saline solutions and measure your refractometer vs. them.
> 
> I know for myself, I would rather be calibrating an instrument to the range of values I expect to see.


Thanks for the link. Didn`t understand most of it  but did understand the last part on how to calibrate. Going to give it a try..


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## Ctp416 (Nov 23, 2011)

altcharacter said:


> Just a side note to this thread. When we calibrated our devices at the BBQ everyone calibrated it to the proper 33ppt that the solution is made of. So, since 4 different refractometers are now reading the same solution @ 33ppt they should all read R/O water at the same level, regardless if it's 0 or 4 right?
> 
> In our case mine was reading 2-3 and a few others were reading 0 and 5-7. I own a Sybon and think it's still working but this just shows that everyone's tool is going to be different


Thanks for the side note. I guess we can never be 100% sure of the salinity but I hope to be close...


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## BIGSHOW (Sep 10, 2011)

Ctp416 said:


> Thanks for the link. Didn`t understand most of it  but did understand the last part on how to calibrate. Going to give it a try..


Let us know how you make out.


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## BIGSHOW (Sep 10, 2011)

altcharacter said:


> Just a side note to this thread. When we calibrated our devices at the BBQ everyone calibrated it to the proper 33ppt that the solution is made of. So, since 4 different refractometers are now reading the same solution @ 33ppt they should all read R/O water at the same level, regardless if it's 0 or 4 right?
> 
> In our case mine was reading 2-3 and a few others were reading 0 and 5-7. I own a Sybon and think it's still working but this just shows that everyone's tool is going to be different


If you read the above article you can see how some meters may read RO water differently. However, calibrating your meter to a saline solution will ensure that the values you are trying to measure (i.e. 1.020-1.026) will be correct.

If you want to use the refractometer to measure the salinity in your RO water then don't calibrate it using a saline solution. If you want your refractometer to be used to measure the salinity of your marine tank, then you need to calibrate it to the proper saline solution.

I don't understand why you would care if your refractometer is reading 0 for RO water. Personally I have never checked and I don't care, as long as it is reading 35 ppm (or whatever the calibration fluid is, temperature compensated of course) when I check it with the calibration solution I am good to go.

I usually purchase a few bottle of the saline calibration solution, and check the refractometer against each of them


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## sig (Dec 13, 2010)

why you guys should complicate everything  and look for the additional ways to spend money 
set to 0.000 using RODI >>> test mix using Refractometer and Hydrometer. Take average value and that it.

I calibrated my Refractometer 20 months ago using RODI and do not care about it anymore.

I also do not care if I have 1.023 or 1.0025. I know different types of tanks/corals require different level of salinity, but somehow it works for me and I have all types of corals

do not forget also that despite you made a mix for 1.023, you will always have different value in the tank, as result of the evaporation and non proper adjusted of ATO, skimmer skims more wet and etc...

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## BIGSHOW (Sep 10, 2011)

You spent more money on buying a hydrometer and a refractometer then I did buying a few calibration bottles.

It may not matter to your system, but that doesn't mean it doesn't matter. 

This is an excellent thread with lots of good information for people to make there own decision on how to calibrate/measure there salinity.

For the people that do care, please keep posting the information you come across with your own personal results.


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## sig (Dec 13, 2010)

Hydrologist said:


> You spent more money on buying a hydrometer and a refractometer then I did buying a few calibration bottles.
> 
> It may not matter to your system, but that doesn't mean it doesn't matter.
> 
> ...


Man, everything that everybody says including me just personal opinion. I am not trying to diminish anybody here and I did " posting the information you come across with your own personal results". Hopefully my result will help people who does not care

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## BIGSHOW (Sep 10, 2011)

Just some more information I stumbled upon on another forum.

This was posted by Fauna Marin

"HI

Sorry guys but there are some things wrong here

Refractometer are made to measure the salinity of Sodiumchlorid luiquids. Not for Seawater. It is of course not correct, to calibrate a test device to the farthest point possible.
Due to the calibration with RO Water/or sodiumchlorid luiquids the refractometer will show a uo to 1.5 points wrong salinity
if you use RO Water it could be more then 2 points wrong.

There is only one correct way to calibrate such a refractometer

1. Clean it well
2. Add a seawater based reference solution on the refractometer
3. Calibrate it then on the ppt chart 35 Salinity ( do not use the other chart which showed density)
4. recalibrate it weekly

rgds claude"

Cheers,
Dave


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## Ctp416 (Nov 23, 2011)

Hydrologist said:


> Just some more information I stumbled upon on another forum.
> 
> This was posted by Fauna Marin
> 
> ...


Thanks for all the info. I`m going to calibrate with the saline solution from here on in and keep an eye on my corals to see if there`s a noticeable difference in appearance. This will drop my salinity by .04


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## Tim (Dec 11, 2011)

Bringing this thread back to life 

I was using the Instant Ocean hydrometer

Now using a refractometer calibrated using sybon 35ppt saline solution (from SUM)


DT water:

Instant Ocean Hydrometer: 1.024
Refractometer 1.03

yikes.

I also tested both with my second tank which contains my mixed water for water changes. I keep it the exact same as my tank.

Instant Ocean Hydrometer: 1.024
Refractometer 1.03

So same readings. 

I am now SLOWLY bring down my salinity in my DT, aiming for .01 reduction per day. My corals have been healthy (softies that can take abuse) so not a great indicator. My chromis over the past while have been stressed and I thought it was due to bullying, but maybe not, so I will keep an eye on them too.


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## sig (Dec 13, 2010)

are you sure it is the same reading . 1.03 is high in my uneducated opinion

http://www.thereeftank.com/forums/f6/how-high-a-salinity-is-too-high-50700.html



Tim said:


> Bringing this thread back to life
> 
> I was using the Instant Ocean hydrometer
> 
> ...


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## Tim (Dec 11, 2011)

I believe so yes.

I started thinking my hydrometer was off when I was having to add way more salt than recommended per gallon.


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## rburns24 (Jan 31, 2011)

Hydrologist said:


> Just some more information I stumbled upon on another forum.
> 
> This was posted by Fauna Marin
> 
> ...


+1

This is correct.


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## sig (Dec 13, 2010)

rburns24 said:


> +1
> 
> This is correct.


that is what I was trying to tell. If your tank is OK, do not worry about it.

I found that when I try to ply more with the chemistry . I screw all parameters more

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## rburns24 (Jan 31, 2011)

sig said:


> that is what I was trying to tell. If your tank is OK, do not worry about it.
> 
> I found that when I try to ply more with the chemistry . I screw all parameters more


Know what you mean. I started Zeovit about 9 months ago and things are just starting to drop into place. In that 9 months I had problems and seemed to be running around in circles at times, but now my two main aims are consistency(not jumping back and forth on my part) and stability.(on my tank's part)

I think I'm just about there, but time will tell.


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## rburns24 (Jan 31, 2011)

P. S. Either way, it's a great hobby, though.


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## Tim (Dec 11, 2011)

Well I had a couple of stressed out fish and one of my others wasn't acting right so I had to consider the possibilities. The chromis are still stressed, but the third is acting a bit better now so I am assuming it was the salinity. I guess I will know better later next week.


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## Tim (Dec 11, 2011)

just a quick follow up. The chromis are now swimming around.  Still acting a tiny bit skittish and not quite as active as they used to be before bottom sitting, but otherwise seem content. Must have been the salinity. Or the constant water changes (1 gal of sw out, 1 gal Ro water in daily + one 5 gal WC + daily top ups with RO)


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## darthvictor (Aug 16, 2011)

btw keep your refractometer in around 77F (25c) when you do the test, same to the testing solution. It scares me when I just pick up my refractometer yesterday and put some tank water to check and it gives me 1.03 because the refractomerter is cold even it has ATC


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