Tropic Marin Hydrometer vs refractometer vs Milwaukee MA887

[mpatterson42]

I recently picked up a Tropic Marin High Precision Hydrometer as it gets very good reviews and does not need to be calibrated. When I first checked it against my reef tank it showed 1.0222, I was surprised it was that low since all my coral seemed to be doing fine, but I decided to raise it using saltwater on my ATO reservoir (measured at 1.025 on the hydrometer). After a week I was surprised it had only raised a little bit, 1.0235. It's 50 gallons of total water volume and I get about a gallon a day evaporation.

I decided to use my other salinity tools to see how they are compared, and both my refractometer and Milwaukee MA887 showed a much higher salinity.

1. Refractometer (Between 1.026 and 1.2027) calibrated with 35ppt calibration fluid

2. Milwaukee MA887 seawater refractometers (1.027) calibrated with 0TDS RODI water.

3. Tropic Marin High Precision Hydrometer (1.0235) in a 500ml graduated cylinder

The water is 80F degrees. I used this site for the hydrometer https://www.hamzasreef.com/Contents/Calculators/SalinityCorrection.php and the actual salinity only goes to 1.0241.

I just don't know who to trust. If I actually get the salinity up to 1.026 on the Tropic Marin I have a feeling the salinity is going to be much higher on the refractometer and MA887, it just seems like too large of a discrepancy. I don't want to hurt the coral of the fish if for some reason it's inaccurate.

Any thoughts on a way to check the Tropic Marin Hydrometer accuracy?

 

[jonelder68]

The TM hydrometer is perfect. It’s all I use. I keep my tank and mixing bin at 77 so no need to temp correct readings. As long as your properly temp correcting reading I would always trust the TM hydrometer. Multiple ICP test have confirmed I’m at 1.026sg.

Also make sure to rinse the TM hydrometer after each use. I just use tap water and then wipe try with a towel.

 

[EricR]

I use and trust the TM hydrometer also but that doesn't mean that an improperly calibrated unit (from manufacturer) couldn't end up out in circulation.

In your case, I'd suggest making a DIY salinity standard for the hydrometer and check it at close to 77 degrees, if you can.

This is a bit of a long read but you can scroll down to near the end of the "Specific Gravity Standard" section:
DIY Calibration Standards

You could also make separate standard for both of your refactometers and check those.

Maybe someone will chime in with consolidated versions.

 

[jonelder68]

Another way to confirm is make a batch of NSW and test the Alk levels. Like I use TM pro reef salt and at 1.026sg it should test at 7.6-7.8dkh. If test lower then you know the salinity is lower then test says. How I confirmed my Hanna digital is complete junk.