Salinity this should be so simple

Aframereef

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Hi a couple years ago I thought I has my salinity too low so I ordered some calibration fluid from bulkreef. I picked up the hanna hi70024. I used this to calibrate my refractometer. After doing so it said my salinity was real high 41ppt. I decided to lower it to 35ppt. At first everything seemed OK but over the last year my 4 urchins died and my 4 starfish. Now my clams are not doing well. Had a temperature sensor go bad and thought it might be copper so I did an ATI test. No copper but my salinity was 23.63ppt. Before I sent the water sample I measured my salinity at 35ppt and checked my refractometer with the hanna solution and it shows 35ppt. Just rechecked my refractometer and a 2nd unit. Both read the same 35ppt for tank calibration fluid.
I am days away from putting salt in my new 400G tank and want to get this resolved. I have had amazing tanks in the past.
When I check my refractometer calibration with rodi water it reads 10ppt. Which is about how much I'm off by.
All I do to calibrate the refractometer is add the 35ppt solution and adjust the set screw until I get a 35ppt reading.
What am I missing????????????
1 pic of the rodi at 10ppt 2 pics of tank water. 2 of hanna solution.

20220930_180747.jpg 20220930_180329.jpg 20220930_175925.jpg 20220930_180117.jpg 20220930_175654.jpg
 
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nezw0001

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Get a hydrometer. I use my hydrometer to periodically check the accuracy of my Milwaukee digital. With the hydrometer there is nothing to calibrate or drift over time. Easy to read as well.
 
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Tim McLellan

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I use a swing arm hydrometer. Very simple device and IMO very accurate as long as you keep it clean with a freshwater cleaning after each use (I just use tap water). No calibration needed, messing with fluids, very inexpensive, it just works. Never have any issues
 

TangerineSpeedo

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It says right on the package ( Hanna HI70024 ) "Not for Refractometers" That solution is for conductivity meters. You would need to get a NSW 35ppt from someone like continuum. There is no way to calibrate your refractometer with that. The best you can do right now is calibrate it with RODI. But that is not even accurate. If you get some 35ppt NSW calibrate to that, If then it matches 0 using RODI you have a good refractometer.
 

Randy Holmes-Farley

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I use a swing arm hydrometer. Very simple device and IMO very accurate as long as you keep it clean with a freshwater cleaning after each use (I just use tap water). No calibration needed, messing with fluids, very inexpensive, it just works. Never have any issues

My testing of two brands did not suggest high accuracy. This is from an article of mine:


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.


For the standard type Tropic Marin hydrometer, I got a 77 °F/77 °F specific gravity of about 1.0265 ± 0.0003 (Figure 4), which compares well to the expected value of 1.0264.
 

WVNed

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I use a swing arm hydrometer as well. When the arm is on the black line I drew with the Sharpie all is good. This isn't any different than calibrating the temperature ring on a heater. I used a calibrated pinpoint conductivity meter to draw the line years ago. The numbers are worn off the hydrometer anyway.
 
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