High Tide Aquatics

How are you measuring salinity?

Chromis

Chromis

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I was given two older hydrometers this week by a coworker who has been out of the hobby for some time... first, note how the recommended salinity range has grown over time! Second, the hydrometers measured inconsistent, the two old ones measured 1.019 and 1.022, while mine measured 1.025 (on some fresh saltwater I was mixing). I have always kept my salinity close to 1.026 because corals just seemed happiest at the higher salinity but I also suspected my hydrometer measured high.

What do I do now that I don't trust the hydrometers anymore - just stick with one, stay consistently at a salinity where corals seem happy knowing I have no idea what the actual level is... or spring for a refractometer or salinity monitor? And which do you recommend?
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Refractometers aren't that expensive. I would trust it far more than a hydrometer. You'll want to get some calibration solution with it. I like the fauna marine reference solution. You'll be able to use it to test against all your other test kits.
 
Refeactometer. Ditch the crappy swing arm asap. Milwaukee digital is nice and easy to use but like $100 instead of $40 for a refractometer.
 
+10000 on the amazingness of a Milwaukee. It was pretty discounted last thanksgiving BRS sale. But I think I have a refractometer somewhere that you can have in the meanwhile. Lemme look after coffee.


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sjbro said:
+1, although the refractometer was pretty good, i love the digital milwakee meter. Much easier to use, specially since I'm getting old and can't trust my eyes anymore ;)
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Agree on the Milwaukee. A tad on the expensive side, but definitely worth it's money. Not as painful on the eyes trying to read the tiny lines on handheld refractometer and doesn't drift after calibration as much as handheld.
 
RandyC said:
Agree on the Milwaukee. A tad on the expensive side, but definitely worth it's money. Not as painful on the eyes trying to read the tiny lines on handheld refractometer and doesn't drift after calibration as much as handheld.
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Refractometers (at least mine) are quite temperature sensitive. Not quite sure why this is, but the temperature of the saltwater you are testing matters. Also, there is significant measurement error if the cover is not reasonably parallel to the prism while you are viewing the reticle.
 
I have a question on calibration. This was an issue Hubby and I had this morning. After calibrating with the 35 solution the RODI water was under 0. Is that possible? Did we get bad 35 calibration solution?
 
LOL!! I have used the same hydrometer for over 10 years. Had another one for the 10 years prior. Never tried anything else. I have heard they are very inconsistent from one another, however using the same one, and staying consistent with what that one says, seems to keep the kritters happy. Don't fix what ain't broke. Ha! Curious what your refractometer would read on my tank.

Question is, what would I do if it said I had the wrong salinity?


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Kim Pattison said:
I have a question on calibration. This was an issue Hubby and I had this morning. After calibrating with the 35 solution the RODI water was under 0. Is that possible? Did we get bad 35 calibration solution?
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Its possible to get a low reading for RODI after calibrating at 35ppt.

This is due to slope error, and it's the reason why you want to calibrate close to the salinity that you will be using.

The further away from the calibration salinity, the greater the difference you will see between measured and actual salinity.

Does not mean the calibration solution was bad.
 
Mr. Ugly said:
Its possible to get a low reading for RODI after calibrating at 35ppt.

This is due to slope error, and it's the reason why you want to calibrate close to the salinity that you will be using.

The further away from the calibration salinity, the greater the difference you will see between measured and actual salinity.

Does not mean the calibration solution was bad.
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Thank you that makes perfect sense

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Refractomers are made to read to read brine, not ocean water like we are replicating, which is why there is a slope error built in to all refractometers. Calibrating with 35 ppm fluid makes it accurate for testing salt water, but not RO/DI water. And vice-versa.

Regarding temperature, it makes a big difference in refractivity of light, but all "good" refractometers include temperature compensation, which should make the temperature matter very little. Make sure you get one with temp compensation.

If you will be using both a refractometer and a conductivity probe like on the Apex, make sure you get a standard solution calibrated that works for both so you can synchronize them. I got the Pinpoint Salinity Calibration Fluid from BRS and it works great, greatly reduced the frustration I was having with trying to calibrate them separately. Don't use the Neptune calibration fluid for this reason (calibrated for conductivity but not refraction).

I agree with the point made earlier that it isn't the absolute accuracy but rather the consistency (precision) that matters for stability in your tank. This is why even an uncalibrated refractometer is infinitely better than a hydrometer.


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