Lesson learned on Salinity

[salty150]

That's actually not very good there are many with higher. One of my complaints about the Milwaukee digital besides how it's calibrated would be I wish it had higher resolution. I'd like to read out to at least the tenths place in PSU mode.

Which ones?

Hanna's is +/- .002 as well...

 

[jason2459]

Which ones?

Hanna's is +/- .002 as well...

That is because it's exactly the same one. Vitalsine and Veegee STX3 is one example if you want one. If you want digital there's many conductivity probes that are easy to use and read that are under that.

Edit: and don't get me wrong I do like the Milwaukee digital. It's very easy for my son to use. But it does have it's limits.

 

[Frop]

I've gotten paranoid with my salinity the last month or more after I began mixing my own salt. I literally use the calibration fluid 2-3 times. Until two results repeat. Maybe the lense still was dirty or something idk lol then I clean everything with RODI after.

Sorry to hear about your loss. Seemed like you handled it maturely.

 

[Klwheat]

I learned the hard way to double, and sometimes triple, check. I have an apex controller monitoring for changes/trends. I use a refractometer that I calibrate pretty much every time I use with 35ppt solution. I check my tank (I know where it should be) and calibrate just to make sure. I also know how much salt it should take to make 35ppt solution. If any of them is off, I get very suspicious.

 

[Alfrareef]

Sorry for step in, but why don't you calibrate with rodi water?
I always do that just before test salt water...

 

[Emmagmrtz]

^^ I do the same. I zero it out with rodi water then use it.

 

[Osiel Alvarado]

I dont get how if you checked your tanks salinity once a week with that ruined refractometer you didn't realize it was off.

 

[Ted_C]

I heard the best salinity refractometer was the vee gee stx-3. I check the calibration every time with pinpoint 35 PPT fluid and it's held pretty good. The only variations I get is when the temperature changes (as expected)

I also use the Apex Lab grade salinity probe in the tank 24x7

https://www.amazon.com/Vee-Gee-Scientific-STX-3-Refractometer/dp/B004WDW70M

Yes, it's more expensive than what you get from the other retailers but it's worth it for the piece of mind.

One other thing I noticed: the salinity standards that come in the bag - I've never gotten these to work out correctly on the Neptune Apex Salinity probe
http://www.marinedepot.com/Digital_...eagent-Digital_Aquatics-DA1379-FITECL-vi.html

I always have to use the pinpoint solution on the probes.

 

[Randy Holmes-Farley]

Sorry for step in, but why don't you calibrate with rodi water?
I always do that just before test salt water...

^^ I do the same. I zero it out with rodi water then use it.

Such calibration with RO/DI can be inaccurate for several reasons.

The first reason is that that many refractometers sold to hobbyists are brine refractometers, not true seawater refractometers. These devices, when manufactured perfectly and calibrated with RO/DI perfectly, will perfectly measure brines (sodium chloride solutions) and will imperfectly measure seawater salinity.

The second reason is that some refractometers may not be manufacturer perfectly, and calibrating them far from the salinity where they will actually be used can amplify the errors. Scientists always calibrate any device near the concentration they will measure, and usually do so at multiple point both above and below the concentration being measured to know the response at the measured concentration is accurate.

So for this reason, using a correct 35 ppt seawater standard to calibrate for measuring 35 ppt seawater can never incorrect to use, while using RO/DI can.

 

[d2mini]

Whether you can trust what they say is anyone's guess, but here is what Red Sea has to say about their refractometer, which according to them, is not the standard brine refractometer.

http://www.redseafish.com/red-sea-salts/seawater-refractometer-salinity-test/

Again, I'm not arguing against using 35ppt calibration fluid, but I see no reason not to follow Red Sea's instructions in this case.

Besides, I still use my lab grade GHL probe for critical measurements, and honestly, it's really not that critical.
As long as my water is somewhere between 1.024 to 1.027 (preferably somewhere in the middle), I don't really care.

 

[MicroPico]

Such calibration with RO/DI can be inaccurate for several reasons.

The first reason is that that many refractometers sold to hobbyists are brine refractometers, not true seawater refractometers. These devices, when manufactured perfectly and calibrated with RO/DI perfectly, will perfectly measure brines (sodium chloride solutions) and will imperfectly measure seawater salinity.

The second reason is that some refractometers may not be manufacturer perfectly, and calibrating them far from the salinity where they will actually be used can amplify the errors. Scientists always calibrate any device near the concentration they will measure, and usually do so at multiple point both above and below the concentration being measured to know the response at the measured concentration is accurate.

So for this reason, using a correct 35 ppt seawater standard to calibrate for measuring 35 ppt seawater can never incorrect to use, while using RO/DI can.

@Randy Holmes-Farley, I wholeheartedly agree, though I do have a question that I hope you can help me with. How can I prevent evaporation in my calibration fluid so it doesn't raise the salinity which would throw off the accuracy of the results? Do I just buy new 35ppt calibration fluid annually?

 

[FindNem0]

I don't get how if you checked your tanks salinity once a week with that ruined refractometer you didn't realize it was off.

I remember checking it after changing water and it being like 1.036 or 1.039 and I was like wow that's hi!! So I just changed another 20 gallons to bring it down. It was also the same night I added Bio blocks and a new skimmer as well as changed salts. I had a lot of moving parts that night. I have never been one to claim I know everything. I made a mistake. I learned from it. In fact I didn't even know that tool needed to be calibrated. All the reefers I talked too none of them talked about calibrating their refractometers. None of them!!! I never thought my refractometer could go out of calibration. Guess what? Of all the reefers including store owners of reef stores and seasoned hobbyist, not one of them mentioned salinity. Not one of them mentioned calibrating a refractometer. My refractometer came from family. When I started doing this hobby, nobody was there to tell me to calibrate my measuring tool. So you say "I don't get how if you checked your tanks salinity once a week with that ruined refractometer you didn't realize it was off" By the time I could realize "it was off" Everything was dead!!! If you ever had a fully stocked aquarium filled with coral and fish, you would realize how fast a tank can crash. The only reason I figured all this out was because I've been trying to cycle two tanks and all my levels are low. DHK6.9,Cal370,mag1200, so I went and bought a new refractometer and tested my water and it was at 1.006. So there may be holes in this and things I may or may have not done, it was 8 months ago. I learned and you can tell by the responses that everyone has their own way of doing things. No right, no wrong when we are all accomplishing the same thing in the end. Post your reefs. Everyone seems to have all the answers. Lets see the reefs you all check that salinity on. I feel like this was a great blog and I'm glad I struck a match. People can learn from this. We are not all top notch reefers. Just a guy who enjoys the hobby.

 

[salty150]

I guess no one has really commented on the best (or a very good) digital one...?

Have had people say they don't like the Milwaukee or Hanna because of its +/- .002.

But which digital ones are more accurate?

 

[Alfrareef]

Such calibration with RO/DI can be inaccurate for several reasons.

The first reason is that that many refractometers sold to hobbyists are brine refractometers, not true seawater refractometers. These devices, when manufactured perfectly and calibrated with RO/DI perfectly, will perfectly measure brines (sodium chloride solutions) and will imperfectly measure seawater salinity.

The second reason is that some refractometers may not be manufacturer perfectly, and calibrating them far from the salinity where they will actually be used can amplify the errors. Scientists always calibrate any device near the concentration they will measure, and usually do so at multiple point both above and below the concentration being measured to know the response at the measured concentration is accurate.

So for this reason, using a correct 35 ppt seawater standard to calibrate for measuring 35 ppt seawater can never incorrect to use, while using RO/DI can.

Thanks Randy for the advise. i have a TMC refractometer (sold few years ago as SW refractometer) and about to question the manufacturer about if that. In the meanwhile i´ll get a calibration set so i can be sure about what i´m using!

 

[jason2459]

I guess no one has really commented on the best (or a very good) digital one...?

Have had people say they don't like the Milwaukee or Hanna because of its +/- .002.

But which digital ones are more accurate?

I did above. I also think the Milwaukee is fine. It could be better.

As far as best will be the one you can use consistently.

 

[TylerS]

I wonder what the user error plus instrument error is on non-digital refractometers?

 

[jason2459]

I wonder what the user error plus instrument error is on non-digital refractometers?

That's easy.

+/-100% of the reading.

 

[Randy Holmes-Farley]

@Randy Holmes-Farley, I wholeheartedly agree, though I do have a question that I hope you can help me with. How can I prevent evaporation in my calibration fluid so it doesn't raise the salinity which would throw off the accuracy of the results? Do I just buy new 35ppt calibration fluid annually?

That could be a concern. If you don't leave it open for long, however, you'll keep it to a level where it shouldn't be a concern. It will evaporate a tiny bit more slowly than fresh water.

You can check with a DIY, and DIY or commercial, if the new one matches the old one, you can use both or give one away.

 

[Desmo996]

So I've had a reef tank for 5 years... Been using the same plastic, low-tech, submersible salinity checker, that I'll bet most of you will say I'm careless for using.
However, Two cups of Red Sea coral pro in 4 gallons of Ro Di water has yielded the same measurements... Always. Hard to argue with consistency... And a successful tank.

So why should I have the high tech one, that needs calibrated, etc, etc... I'm open to the idea but hard to argue against positive results.

 

[Randy Holmes-Farley]

So I've had a reef tank for 5 years... Been using the same plastic, low-tech, submersible salinity checker, that I'll bet most of you will say I'm careless for using.
However, Two cups of Red Sea coral pro in 4 gallons of Ro Di water has yielded the same measurements... Always. Hard to argue with consistency... And a successful tank.

So why should I have the high tech one, that needs calibrated, etc, etc... I'm open to the idea but hard to argue against positive results.

Well, maybe it has been inaccurate all this time? lol

I tested two swing arms for an old article and one was quite inaccurate:

Chemistry and the Aquarium: Specific Gravity: Oh How Complicated! ? Advanced Aquarist | Aquarist Magazine and Blog
http://www.advancedaquarist.com/2002/1/chemistry

from it:

So how do these hydrometers measure up? In my tank the water was measured to be S=35 ± 0.5 by conductivity. Using the Deep Six swing arm hydrometer I got readings of S=32.5 ± 0.5 at 81 °F and S=32 ± 0.5 at 68 °F. Using the SeaTest I got S=34.5 ± 0.5 at 81 °F and S=34 ± 0.5 at 68 °F.