Salinity Measuring-I have no idea which one is correct and what my tank actually is

[Nanorock1970]

So, I originally was using an instant ocean beam style hydrometer to test salinity. Finding out that it has its inaccuracies, I purchased a refractometer on Amazon along with Brightwells calibration solution. I have been using the refractometer to check the salt water I was purchasing from the LFS and my tank figuring all was well at 33-34 ppm after calibrating before each use to the solutions 35 ppm. I am now making my own saltwater for about 4 months now. I am using the refractometer still, calibrating before each use. Well my tank was not doing that great so I decided that maybe my salt concentration was a bit on the high side since I was mixing to 34 ppm and I decided to lower the salinity in my tank over a few days to 32 ppm. So today I decided to check with my refractometer and my hydrometer because my Kenya tree was all drooped over. Refractometer, calibrated before use, still seams to be 34 ppm even though I had added slowly over the course of 3 days, 2 gallons of RODI. I decided to check with the beam and it is reading 32 ppm....SO now I have no idea which one to trust...I tested several times with the refractometer, checking calibration each time and cleaning the surface with fresh water and I checked with the beam several times and both continue to provide the same results. 34 ppm refractometer and 32ppm on the beam...I guess I might not even be looking this closely if the Kenya tree was not showing distress. For the most part, I think everything else looks ok.

 

[landlubber]

So, I originally was using an instant ocean beam style hydrometer to test salinity. Finding out that it has its inaccuracies, I purchased a refractometer on Amazon along with Brightwells calibration solution. I have been using the refractometer to check the salt water I was purchasing from the LFS and my tank figuring all was well at 33-34 ppm after calibrating before each use to the solutions 35 ppm. I am now making my own saltwater for about 4 months now. I am using the refractometer still, calibrating before each use. Well my tank was not doing that great so I decided that maybe my salt concentration was a bit on the high side since I was mixing to 34 ppm and I decided to lower the salinity in my tank over a few days to 32 ppm. So today I decided to check with my refractometer and my hydrometer because my Kenya tree was all drooped over. Refractometer, calibrated before use, still seams to be 34 ppm even though I had added slowly over the course of 3 days, 2 gallons of RODI. I decided to check with the beam and it is reading 32 ppm....SO now I have no idea which one to trust...I tested several times with the refractometer, checking calibration each time and cleaning the surface with fresh water and I checked with the beam several times and both continue to provide the same results. 34 ppm refractometer and 32ppm on the beam...I guess I might not even be looking this closely if the Kenya tree was not showing distress. For the most part, I think everything else looks ok.

if possible, take your water to your nearest lfs and let them test it.
regardless, 1.025 - 1.026 or 35ppm is your goal in a reef aquarium. messing with it is just at the expense of you corals and overall stability.
ps. comparing between a calibrated refractometer and a hydrometer is not a good practice. it makes you not trust either. toss the hydrometer

 

[Randy Holmes-Farley]

What size tank are we talking about that 2 gallons will drop the salinity by 2 ppt? Just want to double check the math.

My suggestion is to make some standards, especially if you have a scale:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

 

[blasterman]

if possible, take your water to your nearest lfs and let them test it.
regardless, 1.025 - 1.026 or 35ppm is your goal in a reef aquarium. messing with it is just at the expense of you corals and overall stability.
ps. comparing between a calibrated refractometer and a hydrometer is not a good practice. it makes you not trust either. toss the hydrometer

Toss bad advice I say.

Get a third party to verify. Go with the majority.

I still use a plastic beam style hydro and have so for years. I've broken one refractometer and lost another. My plastic hydrometer reads within a point of my prior refractometers, does so consistently, and doesn't require calibration. Just tap it to get the bubbles off the arm. Please learn the difference between accuracy and precision.

At my place of business we bought several thermometers for reading skin temps to verify potential fever due to covid. None of the stupid things read the same. Old school bulb thermometer is spot on. Given the advice here I should toss the analog thermometer and go with digitals ...just....because.

 

[landlubber]

Toss bad advice I say.

Get a third party to verify. Go with the majority.

I still use a plastic beam style hydro and have so for years. I've broken one refractometer and lost another. My plastic hydrometer reads within a point of my prior refractometers, does so consistently, and doesn't require calibration. Just tap it to get the bubbles off the arm. Please learn the difference between accuracy and precision.

At my place of business we bought several thermometers for reading skin temps to verify potential fever due to covid. None of the stupid things read the same. Old school bulb thermometer is spot on. Given the advice here I should toss the analog thermometer and go with digitals ...just....because.

no. buy quality equipment to begin with, take care of it, calibrate it if needed and for redundancy check it periodically. advice i've shared because its the consensus of veteran reefers. i didn't come up with this on my own.
just because your anecdotal experience has led you to the place you're at doesn't mean that every hydrometer is the absolute bomb and should be trusted.
if you disagree, fine, to each their own but the fact remains. a calibrated refractometer is the standard for a reason.

 

[Rubblereefer]

I now own 3 instant ocean hydrometers, and a Milwaukee digital refractometer. The 3 hydrometers are all within a point of the digital at most, 2 are spot on, one reads a point off. I have tried other swing arm type hydro meters and they were all way off. I’d say if you go buy a new hydrometer from that brand you can trust it.