Conflicting Salinity results

[Andrew Stevens]

Hello everyone,

I finally had my Waterbox Peninsula 5526 set up on June 4. Since set up, our Apex Fusion has shown levels between 30ppt and 32ppt. I took some water to our aquarium store and they confirmed the salinity levels were low and recommended we add salt.

I added salt on Saturday, and came across a discrepancy I need help with. My Milwaukee MA887 is showing 34 or 35ppt, and my Apex salinity probe is consistently reading around 38ppt. Which salinity level should I trust? And how can I get both measurements to be around the same mark?

Any help would be appreciated, as a first time reefer I don't know what to do. Thanks in advance!!

Andrew

 

[KrisReef]

It’s a wild guess without a calibration solution, something you can make and compare your meter and probes against. Hopefully you can adjust them, at the same time?
Link

 

[gbru316]

1. When you calibrated the conductivity meter on the Apex, did you follow this guide? https://www.reef2reef.com/threads/a...ex-salinity-calibration-and-tc-factor.718971/

2. Do you have a reference standard? Note that because they use 2 different measurement methods (conductivity vs refraction), the reference standards are often not interchangeable.

3. I find that the value of an Apex (and other monitoring equipment) lies not in having real-time quantitative data. Rather, it's value comes from being able to quickly and easily observe trends.

Here's what I would do:
1. Calibrate the Apex using the link above (with the 53,000 uS solution)
2. Purchase refractometer reference solution
3. Test the reference solution with the Milwaukee. If it's adjustable, adjust the Milwaukee so that the reference solution reads 35 ppt (or whatever the reference value is)
4. Adjust tank water using the milwaukee
5. Observe your Apex salinity. Make a note that this is your "normal." If you ever see it drifting or changing significantly, break out the Milwaukee.

 

[Andrew Stevens]

KrisReef and gbru316, thanks for the responses.

gbru316, I really appreciate the step by step. I actually have the refractometer solution for the Milwaukee. I just zeroed and recalibrated, with the solution reading 1.027 instead of 1.025. I'll see if I can make an adjustment to the Milwaukee.

In the meantime, I will purchase some Apex 53,000 uS solution and calibrate using your link.

 

[Randy Holmes-Farley]

Bear in mind that both of these devices have pretty wide uncertainties and will not always agree. The Milwaukee, for example, only claims to be accurate to +/- 2 PSU.

So a reading of 35 PSU (ppt) could be anything from 33 to 37 PSU, even if calibrated and functioning perfectly.