Salinity & Calibration - into the deep end benchmarking calibration solutions

[jafoca11]

I am just getting back into reefing after being out for ~15 years. I bought a generic refractometer from my LFS a couple of months ago and something I wasn't aware to watch out for was how out of calibration a new refractometer can be. Bad (old) newbie mistake, to be sure.

Anyway - in trying to fix the problem, I bought some Fritz calibration fluid and thought that would be that - boy was I wrong!

The first thing I noticed was that my generic refractometer appears to be utter garbage. Readings for the Fritz solution would fall out of line within hours of calibration. This is including waiting for temperatures to equalize and a rigorous rinse/cleaning both before calibration and before readings. The readings swung by more then .003-4 within hours. So - I decided to remedy that problem.

I bought a used Milwaukee seawater digital refractometer off of Ebay - for a bargain price (~$55) and thought that would be that. When it got here I was amazed at the simplicity of using it etc. but then I got the bright idea of measuring my Fritz calibration solution. It showed 1.025. I understand from some other reading on here that the Milwaukee aims for a +-.002 level of tolerance for readings, so that is within margin of error. That said, it was disconcerting to say the least... so...

I bought more calibration solution just to see what is going on. I purchased a bottle of Brightwell Refractometer calibration Standard and BRS Refracto Juice for comparison (not knowing that the BRS solution was manufactured by Brightwell... more on that below).

So... both of those new ones arrived today and I went and tested again. Here are the results:

Fritz: 1.025 / 34ppt
Brightwell: 1.025 / 34ppt
BRS: 1.024 / 33ppt

These measurements were repeatable too. I ran the test at least twice for each solution.

Soooooo... none of them come to the target number, and oddly enough, the BRS and Brightwell have different results despite being the same manufacturer and probably the same recipe/composition.

This all just leaves me wondering - why is this so hard? and from here... should I just count on the Milwaukee to be .002 lower than expected, so aim for 1.028 if I really want a measurement of 1.024?

Lastly - I can't believe that my LFS sold me that junk _without_ calibration solution. I want to support them, but that seems like a pretty bad move. I think I caught it in time for it not to be a major issue with my newish tank, but not a fun experience to go through. I know I bear a lot of the blame for being under-educated there, but still.

 

[GoVols]

Yeah,
Have seen calibration solutions not matching each other.

@Randy Holmes-Farley
Can you post your DIY calibration solution?

 

[wilsonline]

I had similar issues and still have some. After trying some refractometers and that Milwaukee digital refrac, I got the Hanna salinity meter and I'm much happier now. Not perfect, but so practical and precise. Yes, very precise, but you have to check and calibrate to make sure it's accurate. Next to try is the Tropic Marin hydrometer. That one should be a pain to use, but very reliable. At least, that's what I was told. Hanna will still be my number one for its good precision and practicality. I also have the PinPoint which is more precise than the Hanna, but it's a pain to use and has issues with interference bc of the long cable.
I calibrated my Hanna yesterday. I should have mixed saltwater at 35 ppt to store a large 2 l bottle to always have a cheap calibration solution, but I was lazy but going to do this today.

 

[jafoca11]

Yeah it is interesting. I think I have continued to get somewhat unreliable results from the Milwaukee. I am finding that I am measuring, cleaning, measuring, cleaning at least 2-4 times to get what I think is a reliable reading.

I may invest sooner or later in the Hanna salinity meter HOWEVER if you go reading around here, you will see that many people complain about very similar things with that, too, and there does not seem to be definitive agreement that a Hanna is more precise than a Milwaukee. Based on the specs, the Hanna is supposed to have less margin of error than Milwaukee, but people also report that it calibrates / measures somewhat lower readings than other tools, as well. So... /shrug.

It's pretty disappointing to me that it is so hard to get reliable measurements of something so basic for keeping our stuff alive!

 

[KStatefan]

http://www.reefkeeping.com/issues/2004-06/rhf/

 

[Red_Beard]

If you really want to be sure, you are going to have to get away from digital stuff, they all have a large tolerance range. The hydrometer that tropic marin makes would be a better "standard" that you could compare your DRO(digital readout) to. It is accurate to .001, requires no calibration, just temperature compensation.

 

[SquattingSnail]

I am still new with the saltwater aquarium side of things but have a quite a bit experience with water testing... that being said I have both a cheap refractometer and the Tropic Marin Hydrometer. I never use my refractometer. I have a large graduated cylinder that i fill up hold over the sump while I put in the hydrometer, set down the graduated cylinder and wait for the bobbing to stop and take a reading. I also keep my tank at 77 so no temp compensation needed. It is super easy to use.

 

[jafoca11]

I am still new with the saltwater aquarium side of things but have a quite a bit experience with water testing... that being said I have both a cheap refractometer and the Tropic Marin Hydrometer. I never use my refractometer. I have a large graduated cylinder that i fill up hold over the sump while I put in the hydrometer, set down the graduated cylinder and wait for the bobbing to stop and take a reading. I also keep my tank at 77 so no temp compensation needed. It is super easy to use.

Forgive me if I missed something, but how can you avoid the temp compensation req when working with it this way? I thought the point was for the instrument and sample water to come to a similar temperature, so unless you store your hydrometer at 77, it still would need to compensate?

If you really want to be sure, you are going to have to get away from digital stuff, they all have a large tolerance range. The hydrometer that tropic marin makes would be a better "standard" that you could compare your DRO(digital readout) to. It is accurate to .001, requires no calibration, just temperature compensation.

That's the problem, really - the best digital equipment we have seems unreliable / inaccurate, and even the calibration solution we can purchase seems to be inaccurate, so I guess going to something like the TM one, if it is proven to be accurate, is the best option.

 

[mikereefing]

I have so many issues with calibration solutions from manufacturers. I've used AccuBrate and Aqua Craft on Amazon and the results varied by 0.002. I have also tried the Brightwell and lo and behold...it also varied by the same amount. I tested all these at the same time, RODI cleaned and wiped between each test, and with 2 different refractometers. Over time, I noticed I would have to calibrate almost daily when I used the AccuBrate solution because the values would change. Anyway, this was annoying but I didn't think there were any problems with the solution. It wasn't until I tried a Hanna salinity checker for the first time did I notice my salinity was actually 1.024 instead of 1.026. That hanna checker died within a day of use (it was absolutely useless...the salinity would keep dropping to 1.000 when in tank water). I did an ICP test and verified that my salinity was at 1.024.

It turns out that the calibration solution from AccuBrate would have inconsistent results despite shaking between each use. In the end, I tried Randy's DIY recipe for making the solution and it has been SPOT ON every single use.

 

[coralfishreef]

I have the Milwaukee digital refractometer and I barely use it because of the margin of error. However, the Milwaukee is very easy to calibrate because it uses distilled or RODI for calibration instead of a calibration solution.

The glass hydrometers are reliable because they don’t change or drift. As long as they are correctly calibrated from the factory, they are going to be the most accurate for measuring salinity IMO. I’d stay away from the cheap $10 glass hydrometers and stick with the Tropic Marin one. The $10 Amazon ones don’t offer the level of precision.

Because of AWC, I usually check tank Salinity at least 2-3 times a week with a refractometer and also weekly verify the refractometer is still calibrated with the TM Hydrometer.

 

[wilsonline]

I have so many issues with calibration solutions from manufacturers. I've used AccuBrate and Aqua Craft on Amazon and the results varied by 0.002. I have also tried the Brightwell and lo and behold...it also varied by the same amount. I tested all these at the same time, RODI cleaned and wiped between each test, and with 2 different refractometers. Over time, I noticed I would have to calibrate almost daily when I used the AccuBrate solution because the values would change. Anyway, this was annoying but I didn't think there were any problems with the solution. It wasn't until I tried a Hanna salinity checker for the first time did I notice my salinity was actually 1.024 instead of 1.026. That hanna checker died within a day of use (it was absolutely useless...the salinity would keep dropping to 1.000 when in tank water). I did an ICP test and verified that my salinity was at 1.024.

It turns out that the calibration solution from AccuBrate would have inconsistent results despite shaking between each use. In the end, I tried Randy's DIY recipe for making the solution and it has been SPOT ON every single use.

so Hanna replaced your checker? if it died with one day of use, they will replace it.

 

[mikereefing]

so Hanna replaced your checker? if it died with one day of use, they will replace it.

This was my second attempt at this checker actually. Hanna seriously needs to sort out the salinity checker QC. I ended up returning it and getting a refund. I was chatting with the online store rep and it turns out that the checker gets returned very frequently.

 

[KStatefan]

That's the problem, really - the best digital equipment we have seems unreliable / inaccurate, and even the calibration solution we can purchase seems to be inaccurate, so I guess going to something like the TM one, if it is proven to be accurate, is the best option.

What are you considering the best digital equipment? I know @Randy Holmes-Farley recommends the Orion model 128 if you can find a used one on Ebay. Is there a new model available that is good or another brand like the Oakton?

 

[SquattingSnail]

Forgive me if I missed something, but how can you avoid the temp compensation req when working with it this way? I thought the point was for the instrument and sample water to come to a similar temperature, so unless you store your hydrometer at 77, it still would need to compensate?

The compensation would only be needed if the temperature of the measured liquid differed from the factory calibration temperature. The water is 77 degrees. Putting the hydrometer in the water will change the temperature of the measured volume some but not enough to matter IMO. Sort of getting to an observer effect situation....

 

[rob taft]

I use the Milwaukee and the Tropic Marin much like the way CoralReefFish does in his/her post. My Milwaukee runs about .001 higher than the Tropic Marin. I use the Tropic Marin when I make water for water changes and I use the Milwaukee for routine DT measurements. I don't worry about Temp compensation as the swing between 77 degrees and where my tanks usually sit at (78 degrees) is not an appreciable difference. See link below.

http://reefkeeping.com/issues/2004-07/rhf/index.php