Can You Trust Your Refractometer (and Calibration Solutions)? We Put 3 Tools to the Test | SR LABS
Salinity seems simple… until you realize how easy it is to get wrong.
Between refractometers, calibration solutions, temperature, and technique, it is surprisingly easy to feel confident in numbers that are not actually accurate. In this SR Labs test, we put three popular refractometers and multiple “reference” solutions to the test to answer one question:
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Below is a 60 second preview of: Can You Trust Your Refractometer (and Calibration Solutions)? We Put 3 Tools to the Test | SR LABS
Quick Links:
D&D Refractometer: https://bulkreefsupply.sjv.io/gRogkA
BRS Refractometer: https://bulkreefsupply.sjv.io/o4Kg6o
Milwaukee Digital Refractometer: https://bulkreefsupply.sjv.io/rEgOov
Tropic Marin Precision Hydrometer: https://bulkreefsupply.sjv.io/5kjYP2
SR Merch: https://serious-reefs.checkoutstores.com
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What can reefers actually trust?
What We Tested
D&D True Seawater Refractometer (~$70)
BRS Refractometer with light (~$36)
Milwaukee Digital Refractometer (~$155)
We also tested multiple calibration approaches, including DIY and commercial solutions.
The Big Questions
Are refractometers actually accurate?
Does digital convenience sacrifice accuracy?
Can you trust included calibration solutions?
How We Tested
We validated each tool against three independent 35 PPT reference solutions:
Lab-grade conductivity-created seawater
DIY solution (Randy Holmes-Farley method)
Hydrometer-derived reference (Tropic Marin)
If everything worked perfectly, all tools would match all references. What actually happened was much more interesting.
Key Takeaways
1. Calibration and reference solutions are the weak link
Several “reference” solutions were significantly off. Some tested as high as ~39 PPT when they should have been ~33–35 PPT.
2. Refractometers can be accurate… if calibrated correctly
The D&D, BRS and Milwaukee units performed well after recalibration using reliable inputs.
3. DIY or trusted reference solutions beat meanufactur’s solutions
The most consistent results came from making your own reference or validating against a trusted method.
4. Digital vs analog
Digital (Milwaukee): easiest and most repeatable
Analog (BRS/D&D): accurate but more technique-dependent
5. A 1 PPT error ≈ 3% shift
1PPT off was the worst we experienced. That sounds big, but in practice it is often within the noise of hobby-level testing. Stability matters more than perfection.
Practical Recommendation
Make or verify your own 35 PPT reference
Calibrate with confidence, not assumptions
Let samples sit ~15 seconds before reading (temperature matters)
Focus on consistency over chasing perfect numbers
