How are you checking salinity?

[Robink]

I check my refractometer with the calibration fluid every week before I use it.

 

[Cjp63]

Tropic marine floting hydrometer. The most acurate and also never needs calibrating. The best.

 

[swimer499]

Basic refrac. And I also have a digital one

 

[Forsaken77]

I use a Milwaukee Digital myself because it's easier, but with one major caveat... They say to only use their calibration fluid (which you get a tiny bottle of when you buy it), but you can't buy it anywhere. Also, my calibration fluid bottle was .006 off.

I sent my meter in for warranty repair and it worked properly, it was the fluid that went bad after a while.

 

[Maritimer]

When I just want a quick check, the swing-arm goes into action, but if I want precision, the refractometer comes out to play.

~Bruce

 

[Randy Holmes-Farley]

I use a Milwaukee Digital myself because it's easier, but with one major caveat... They say to only use their calibration fluid (which you get a tiny bottle of when you buy it), but you can't buy it anywhere. Also, my calibration fluid bottle was .006 off.

I sent my meter in for warranty repair and it worked properly, it was the fluid that went bad after a while.

You are saying the fluid went from something like 1.025 to 1.031?

You need to have let 20% of the volume evaporate away.

 

[dougdog]

I've always used refractometer. Everyone I asked told me to calibrate it with RO/DI water so I was doing so for more than a year. My apex always was reading low on salinity no matter how many times I calibrated it. I read some people say Apex salinity probe is not very reliable so I thought I'll go with what the refractometer says because is more accurate. I always had issues where I had new corals dying, losing color or not doing very good overall. One day I saw one of this refractormeters calibration solutions and bought one. My salinity was at 28ppt this entire time. I bought new calibration solution for my apex salinity probe and sure enough the calibration was off this entire time also, maybe from calibrating it with a bad batch of calibrating solution. I slowly increased the salinity to 35ppt and all my corals are slowly getting their color back. Some of them are recovering at an incredibly fast pace. So moral of my story is you should use a calibrating solution on you refractometer. I usually leave the solution on the refractometer for about 5 minutes to compensate the temperature, it makes the difference with about 1-2ppt with temperature changes.

 

[liveround69]

I use a Milwaukee digital and as long as you rinse off the testing pan every time you shouldnt have many problems out of it. I used to have the old style swing arm hydrometer but stopped using them as i noticed that even though you thought you were spot on a certain salinity you would find out that it was a simple matter of the swing arm meter having a large rounded tip which made it hard to decide where exactly it was pointing. This could make it more of a guess than a measurement. I lost some livestock due to salinity issues over those kinds of meters and migrated to the digital. I havent lost a single creature since the switch.

 

[liveround69]

I use a Milwaukee Digital myself because it's easier, but with one major caveat... They say to only use their calibration fluid (which you get a tiny bottle of when you buy it), but you can't buy it anywhere. Also, my calibration fluid bottle was .006 off.

I sent my meter in for warranty repair and it worked properly, it was the fluid that went bad after a while.

Just contact the support dept a few times per year and ask for the calibration kit. They will mail it out to you at no charge. They are very helpful people. It comes with all the stuff you need to recalibrate it. Also dont forget to clean it every so ofter with a little vinegar and rinse the pan out well afterwards.
By the way never use RO water to zero it. RO water most always causes the meter to be calibrated improperly. Thus messing up your reading.

 

[Randy Holmes-Farley]

By the way never use RO water to zero it. RO water most always causes the meter to be calibrated improperly. Thus messing up your reading.

If we are talking about the Milwaukee MA887, there's not reason normal 0 ppm TDS (or even 1 or 2 or anything close to 0 ppm TDS) RO/DI water won't work for 0 ppt (psu) calibration, and whether you trust me or not, Milwaukee says so explicitly in their intruction manual, page 9:

http://www.milwaukeeinst.com/site/db/doc/manma887_20_10_2009.pdf

"Using a plastic pipette, fill the sample well with distilled or deionized water. Make sure the prism is completely covered."

 

[liveround69]

I talked to the technician at Milwaukee instruments and he told me to " use steam distilled water only to calibrate it". He also said for me to "NEVER use RO water to zero the meter." If you have some sort of issue with those statements then simply call them and try to convince them. I am doing what he told me to and i have never had a problem since performing the method he suggested.

 

[Heuristic]

Taste test it!

jk, I just use a refractometer. Simple, reliable and cheap.

 

[Aaron J Henning]

Milwaukee digital. I calibrate once a month.

I do as well. And it has been spot on for the past 5 months. I keep it in the case. And wipe the lense down as soon as the reading is complete. "Clean Equipment, is Happy Equipment!"

 

[Randy Holmes-Farley]

I talked to the technician at Milwaukee instruments and he told me to " use steam distilled water only to calibrate it". He also said for me to "NEVER use RO water to zero the meter." If you have some sort of issue with those statements then simply call them and try to convince them. I am doing what he told me to and i have never had a problem since performing the method he suggested.

He's simply wrong.

What you are doing isn't incorrect, but the statement that RO/DI is not suitable is incorrect.

As an aside, many technical reps that support the products we use do not fully understand them.

 

[Tek]

My next purchase will be a digital salinity. I have had a few refractometers go bad and would like reliability and a backup.

Anyone have experience with Milwaukee vs Hanna?

 

[bo0sted2g]

I use a basic refractometer. was cheap and accurate.

 

[Midrats]

A twenty-year-old Instant Ocean swing arm hydrometer that I compare to a high quality floating hydrometer every few years.

 

[VelasCorals]

usually by taste

 

[Forsaken77]

He's simply wrong.

What you are doing isn't incorrect, but the statement that RO/DI is not suitable is incorrect.

As an aside, many technical reps that support the products we use do not fully understand them.

Hey Randy... I know what it says in the instruction book and have also talked to the technician that repairs broken units. They don't want people using RODI water because they can't guarantee that people are using 0 tds water and may throw the calibration off. Which is why they now say to use distilled, which guarantees 0 tds, even though it's not in the manual.

 

[Randy Holmes-Farley]

Hey Randy... I know what it says in the instruction book and have also talked to the technician that repairs broken units. They don't want people using RODI water because they can't guarantee that people are using 0 tds water and may throw the calibration off. Which is why they now say to use distilled, which guarantees 0 tds, even though it's not in the manual.

You'd have to be far, far, FAR off for it to matter. That's what I expect the tech reps do not understand.

The unit claims +/- 2 ppt uncertainty, but lets suppose we want +/- 0.01 ppt uncertainty from the zero point calibration. Seems crazily precise for a device with such poor precision claims, but let's assume that's what we want. We can easily determine how much TDS could be in the blank water to cause that tiny, tiny error (and no more).

In fact, even without going through the trouble of determining what change in refractive index would lead to a 0.01 ppt error, we can estimate it, to be about 0.01 ppt. Refractive index is essentially linear with ions in it (at least at these concentrations). So that 0.01 ppt estimate is pretty good.

0.01 ppt freshwater has a TDS of roughly 0.01 ppt = 10 ppm. In other words, since refractive index is linear with ions in it,a nd since the error int he blank is only as much as the ions present in it, then if we are willing to "only" allow a 0.01 ppt error in salinity from errors in the blank, we can use fresh water with a TDS up to about 10 ppm TDS. [that assumes this is normal RO/DI and not something made some other way, such as by mixing vodka and distilled water ).

So if the TDS of the tap water is 10 ppm TDS or less, the error that it causes in the salinity measured by refractive index is about 0.01 ppt, which is vanishingly small in a unit that only reads to whole ppt and claims an inherent accuracy of +/- 2 ppt.

As a thought experiment, suppose your tap water has 200 ppm TDS in it. Don't purify it at all and use it as the blank.
How far off is the error? Not much. Real 35.0 ppt seawater would erroneously read 34.8 ppt. Still small compared to the claimed accuracy.

Here's one reason to use very low TDS water (like 0 ppm TDS or distilled):. It's not because it causes errors when used, but because allowing such liquids to dry on the device might leave deposits that will ultimately mess with the readings.