# Salinity Calibration Solutions



## twobytwo (Oct 25, 2014)

Ok, I need a little help here. I want to make my own... Been looking at articles and in the middle of the summer, all this math is hurting my brain.

Basically, I have a standard refractometer and a Milwaukee Digital. Last night I was checking with commercial calibration fluids I have, on the Milwaukee:

TLF Accurasea - read 1.027
Pinpoint 35pt solution - Read 1.030!

What's YOUR recipe for using table salt to create a small amount of solution? The articles I've read talk about 1 litre plus... .I just want to make less than a cup full.

*note: the Milwaukee calibrates with RODI to 0.00 so I am hesitant to calibrate my ATC Refractometer with a calibration fluid that I'm not confident is accurate.


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## rayjay (Sep 6, 2014)

If your refractometer is a salt water refract. then calibration at zero will produce errors at normal salt water aquarium salinity.
If it is a seawater refractometer then it should be reasonably close. 
IMO, it would always be best to calibrate at or near the range intended for measuring.
http://reefkeeping.com/issues/2004-06/rhf/index.php for DIY standard
http://reefkeeping.com/issues/2006-12/rhf/ for general info on refractometers.


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## twobytwo (Oct 25, 2014)

Thanks Ray,

I saw the Randy Holmes Farley articles. I started to calculate differences for a smaller amount (I dont want to make 2.1 litres, too much for me!) but gave up once I was getting into fractions of grams or ml for salt to use.

I fully agree, I would never calibrate a handheld refractometer with anything but a solution at what I'm trying to measure (35psu). Unfortunately, my digital is not giving me much confidence that the commercial fluids which I want to use to calibrate the handheld one with, are at 35. 

I'll double check tonight if my handheld is Saltwater or Seawater. The Milwaukee is the Green one - I have been quite happy with it's ease of use (great for multiple tanks) over the handheld.


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## rayjay (Sep 6, 2014)

I have to be honest with you, I've NEVER owned a refractometer. I've been using one seatest box hydrometer since Jan 94 as well as another newer one I bought a few years after than. When I started, refractometers were not used or even available to the hobby around here.
When they did start becoming more popular, I did some research and found that first of all, there were only salt water and not sea water refractometers available, but most of all I looked at the accuracy of most of the refractometers and found that they usually ran at +- .002 or +-2% salinity. 
Even when the seawater ones came onstream, I didn't see a lot better accuracy in them either, but I do remember seeing one that specified +-.001.
My box swing arm hydrometers are cleaned overnight in white vinegar weekly, and rinsed after every use, and while I checked calibration maybe once a month in my earlier years, I've only checked them anymore just once a year as properly used/maintained I never had any change.
I'm fortunate that I used to work in a lab many many years ago and still had a set of certified calibrated lab hydrometers so I used the appropriate one of the set to check the calibration of my hydrometers with that. A properly used certified calibrated hydrometer doesn't err. (I did break it eventually and bought a new certified calibrated hydrometer from Fisher Scientific)
Anyway, bottom line is I didn't buy one as what I had worked just fine.
Also, IMO, I don't have need of "exact" accuracy anyway. For me, the main point is that I don't allow the s.g /salinity to drift, thinking that more damage could be done by variances rather than specifics. I believe that a lot of reefs probably experience a range of salinities due to local conditions so I may even be wrong on that one also, but I wouldn't want, say, a long term elevated salinity, or long term lowered one for some inverts and corals, even though most fish would likely tolerate it.


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## wtac (Mar 17, 2006)

All the refractometers are based on those used for brining (NaCl) and sugar (brix), where "pure" solutions used will have a constant refractive index. Where it comes to seawater, it's not a "pure solution" so the gradient/scale for a seawater refractometer (ie. D-D) is adjusted based on an average of a large sample set whereas everybody else (ie. Sybon and Milwaukee) the gradient is based on a pure NaCl solution.

The %error, IMHO/E, is insignificant (0.001-0.002 diff) if one keeps the salinity @1.024-1.025. Back in the 90's the ideal salinity was 1.021 and I knew of those that were keeping successful softie and LPS reefs at that time. SPS...yeah you need the higher salinity.

The important thing is consistency when it comes to water parameters so don't get hung up on equipment.

JM2C/E


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