Measuring Salinity

[greg 45]

Boomer I use a Milwaukee Refractometer. My question or concern is that I sent out a triton test and they stated salinity was a tad bit low. How did they come up with this . Did they add which two or three parameter together to get this results. Also which system might be better . Can you please provide the formula for doing so.
Thank You

 

[Boomer]

What is a tad bit low ? The Milwaukee meter is a reboxed Hanna. You CANT go by the decimal place digits called Resolution. You must go by the Accuracy.

What does that mean?

Pretend the meter reads 34.6. That .6 is Resolution in 10ths. The Accuracy of this meter is +/ - 2 ppt. Read your data sheet,it will show you that in the meters listed parameters.

So, if the meter reads 34.6, they are guaranteeing that your Salinity is some where between 32.6 - 36.6 and you don't know where. That is a 4 ppt spread, which is a lot. Even Refractometers and Hydometers are better @ + / - 1 ppt. A 2 point spread.

This means that in theory if the Triton was + / - 1 ppt and your Milwaukee +/- 2 ppt.

The Triton could give you a 33.46 and your Milwaukee a 36.6 in the same sample.

The only way around this is to calibrated your meter with a know std, like the one Julian has out now through TwoLittle Fishes, called AccuraSea Seawater Reference Calibration Solution. This is lab tested as a calibration solution using NSW. This is the only std I stand behind for this hobby, as I know what it goes through and who is envolved.

You then calibrate your meter to that std. And each time you use it check its calibration. This makes your meter much more accurate and believable. Let's now pretend you want to run a tank @ 31 ppt. You should,by rights, get a std for that. As a meter reading moves away from its calibration point, the error factor and its inaccuracy is more pronounced.

 

[BioMan]

Is simply putting "Boomer" in your opening sentence the same as the Bat Signal?? I actually read Boomer's threads when I want to learn something!

 

[Boomer]

Triton is prob probably using a Conducivity Meter and not a Refractometer. A conducitivity meter is the Sea Water std for measuring Salinity. It measures the ability for water to conduct electricity and the higher the conductivenss the higher the Salinty. NSW at 35 ppt and 25 C has a Conductivity of 53,064 ?S / ?mho.

 

[Boomer]

PS

People often get this silly notion that because it is a meter and reads in decimal fractions it must be more accurate....NOT..in many cases.

 

[greg 45]

Boomer more info than expected. I will purchase standard solution. I also have a hydrometer home . I will check it with that tonight. I was reading 1.026 they were stating I was lower adding some numbers from the test . I will try and get that info. I didn't realize the meter was that far out .
THANKS

 

[greg 45]

Last night after checking salinity with a sera old school bobber type hydrometer and it matched the Milwaukee . It might have been luck. I never trusted the ghl salinity probe or the hand held refractometers. Still going to purchase the Julian solution for a reference.

 

[clasystems]

I have been using the Milwaukee unit for years. I calibrated it 1 time and check it from time to time with RO water, never drifted off zero. What I have found is you cannot let saltwater sit on the glass and dry out so its necessary to clean it with fresh water every use. Since getting the Apex salinity probe Ive noticed its all over the place yet the Milwaukee is consistent.

 

[greg 45]

So true clasystems . I don't trust the probe with any of the controllers. Just want to see what boomer's thoughts were . I never expected a big swing in the correction factor from the unit.

 

[Boomer]

Clasystem

You should never calibrate a refractometer with RO/ DI water but a known NSW calibration solution. You are correct always clean the glass. It is best with RO/DI after each use, as the seawater left on the glass will evaporate and leave behind hard water deposits. Good to clean the glass and cover plate once in awhile with Vinegar and rinse every well in RO/DI water.

The reason your Apex salinity probe is all over the place is it is a conductivity meter probe which are quite sensitive. You should get some probe clearer solution and clean it once a month. Algae can grow on these probes or any probe, to include organic accumulations and even hard water deposit, which can off set the meter more, as it is always in the water. If you get some probe cleaner then use that too on the refract. I will add you could use just Vinegar on both but you need to rinse them very well, not needed with probe clearer or just get some pH 4 calibration solution, which basically is what probe cleaner is. You can also make your own with diluted HCl. And use cotton Q-Tips to clean them and not a dam toothbrush or go to hobby shop and pic up one of those containers that have different size and types of little paint brushes.

 

[clasystems]

I tend to gravitate to the easier method that's going to give me reasonably close results. There is one thing I know in the 15+years keeping marine life is that I'm losing interest in the maintenance and upkeep of all these systems.