10 Mistakes Beginners Make Using a Gem Refractometer (and How to Avoid Them) Learning to use a gem refractometer is one of the most important steps in gemstone identification. Instruments such as the GIA Duplex II Refractometer and the GRM-700 Gem Refractometer allow gemologists to measure a stone’s refractive index (RI)—a key optical property that helps identify gemstones quickly and accurately. However, beginners often encounter confusing readings or inconsistent results. In most cases, the problem is not the instrument, but simple technique errors. Below are the 10 most common mistakes beginners make when using a gem refractometer, along with practical...

How to Use a Gem Refractometer (GIA Duplex II & GRM-700): A Practical Guide for Accurate Gemstone Testing Gemologists rely on several diagnostic tools to identify gemstones accurately, but one instrument consistently stands out as the most powerful first test: the gem refractometer. With instruments like the GIA Duplex II Refractometer or the NI Supply GRM‑700 Gem Refractometer, a trained gemologist can quickly determine a gemstone’s refractive index (RI)—a property that often narrows identification to only a few possibilities. However, learning to use a refractometer correctly requires patience, practice, and comparison with known gemstones. The most successful gemologists develop their...

Why a Salinity Refractometer Is Essential for Measuring Bilge Water Before Marine Discharge Marine vessels of all sizes—from small recreational boats to commercial ships—generate bilge water as part of normal operation. This mixture of water, oil, fuel residues, detergents, and other contaminants accumulates in the lowest compartment of a vessel. While regulations require that bilge water be treated before discharge into the ocean, accurate measurement and monitoring remain critical for protecting marine ecosystems. One often overlooked yet extremely valuable tool in this process is the salinity refractometer. Though commonly associated with aquariums, aquaculture, and laboratory work, a salinity refractometer plays...

The Complete Guide to Measuring Reef Aquarium Salinity with a Refractometer (2026)

Maintaining stable salinity in a reef aquarium is one of the most important factors in keeping corals, fish, and invertebrates healthy. Natural ocean water contains a very consistent salt concentration, and even small deviations in your aquarium can cause coral stress, reduced growth, or fish health issues.

For this reason, reef aquarists rely on precise tools to measure salinity. While several methods exist—including hydrometers and digital meters—most experienced hobbyists agree that a refractometer is the most reliable and practical tool for measuring reef tank salinity.

The most accurate way to measure reef tank salinity is with a calibrated refractometer. Reef aquariums should maintain a salinity of about 35 parts per thousand (ppt), which equals approximately 1.026 specific gravity at 77°F (25°C). A refractometer measures salinity by analyzing how light bends through saltwater, providing more precise readings than traditional hydrometers.

If you brew beer, make wine, or ferment kombucha, a Refractometer is one of the most important tools you can own.  Find the best Refractometer for your needs and use the handy interactive Brix, SG, Plato & alcohol correction correction calculator for future reference!