Salinity Reading Question

[fishy27]

I just bought the Milwaukee MA887 digital refractometer. It was getting hard to read my old Refractometer with light so I decided to upgrade. The question I have is I calibrated it to There directions. When I tested my Tank I'm getting a reading of my tank of 1.031. That's when I questioned if it was accurate so pulled out my old Hydrometer and 2 Refractometers (one 3 years old and other maybe 2 years).
The Milwaukee was calibrated with there solution of 1.025 which read actually 1.026. The refractometers where calibrated with Brightwell 1.026 calibration fluid that expired 8/21, not sure if this Matters. I then tested Brightwell calibration fluid in my new Milwaukee and reading where 1.033 or 44 ppt. This is when I started to think if the calibration fluid is bad or the Milwaukee is just not accurate. I was looking to see some other experiences or what reading other would go with?

This is the results
Milwaukee Digital Reading 1.031
Old School Hydrometer 1.029
2 refractometers 1.024

 

[vetteguy53081]

Before lowering, take a sample of water to a trusted LFS and have them test and see what they come up with

 

[fishy27]

Yes Definity do that before dropping it low.

 

[Randy Holmes-Farley Verified Community Expert]

The Milwaukee was calibrated with there solution of 1.025 which read actually 1.026. The refractometers where calibrated with

I presume this means "checked" with that fluid, right, not "calibrated" with it, which in this case can only be done with pure fresh water.

What fluid was it?

 

[fishy27]

Correct. I wanted to see what reading I would get with the calibration fluid.

 

[fishy27]

The Milwaukee comes with 2 bottles one distilled to zero out and other for 1.025.

 

[Randy Holmes-Farley Verified Community Expert]

The Milwaukee comes with 2 bottles one distilled to zero out and other for 1.025.

What exactly does the 1.025 say on it? That's a bit odd of a calibration fluid since it is not 35 ppt. Maybe it is not sg = 1.025 seawater equivalent.

 

[fishy27]

I’m thinking the my brightwell calibration fluid went bad It expired 8/21. I went out and bought a glass floating hydrometer. I calibrated the refractometers with the solution that came with the Milwaukee. All the readings where within 1 point range of each other.

Milwaukee Digital Reading 1.031
Old School Hydrometer 1.030
2 refractometers 1.029
Floating hydrometer 1.029- 1.030

 

[Randy Holmes-Farley Verified Community Expert]

The calibration fluid would only go bad if it evaporated (and hence got more concentrated, making readings based of it read too low).

But Brightwell is not on my list of companies I trust, and it may just have been mismade initially.

 

[fishy27]

I’ve been gradually getting salt back down based on my new readings. My salt was probably high for a while because was using the brightwell for calibration,but time will tell. What calibration fluid are you using? Thanks for your input.

 

[Randy Holmes-Farley Verified Community Expert]

I’ve been gradually getting salt back down based on my new readings. My salt was probably high for a while because was using the brightwell for calibration,but time will tell. What calibration fluid are you using? Thanks for your input.

I use commercial fluids for science labs (made by Oakton for conductivity meters), and my DIY fluids.

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