Salinity Help

[craymond]

Need some advice.

I’ve been using a refractometer for years (fairly expensive back in the day); the instructions read to calibrate with RO/DI. Calibrated with RO/DI my tank salinity is 35%.

I also have the APEX w/Salinity module. I’ve calibrated it several times and replaced the probe but find that swings depending on where in the sump I place it. Placing the probe in a beaker of tank water the APEX reads ~37% salinity.

Not sure which is correct, and after reading some R2R salinity threads, I purchased calibration solution to see if the variance is due to the refractometer. After calibration the refractometer had my tank salinity at 32%. & RO/DO water, on the solution calibrated refractometer reads -0%

So, I don’t know what to trust…

RO/DI calibrated refractometer that reads 35%
APEX salinity module that reads 37%
Solution calibrated refractometer that reads 32%

Anyone have similar experience or have recommendations?

 

[ReeferEric]

I would borrow a local reefer's refractometer to see how it goes. Sometimes these older units develop rust on the flip part (clear plastic piece held together by metal hardware). It can affect the reading. That's the only thing that I can assume that would throw things that off.

 

[Reef Breeders Verified Sponsor]

If you calibrate with rodi water, it will not be accurite. Try using the calibration solution to calibrate your refractometer.

 

[ReeferEric]

If you calibrate with rodi water, it will not be accurite. Try using the calibration solution to calibrate your refractometer.

The OP already did and got different results altogether.

 

[CJO]

I agree with Eric. Also, I'm very surprised that your salinity meter fluctuates that much unless you have it near the heater or ATO feed.

CJ