It’s been a looooong time since Dupla made waves in the reef hobby outside of Europe but its new Dupla Marin Hydrometer, a new high-precision and accurate hydrometer, might get them back on the map. You may be asking yourself “why do I need a hydrometer when I’ve been using my refractometer for years?” but in recent years we’ve seen a gross misunderstanding about long term use and maintenance of the light-bending salinity measurement tools.
The Dupla Marin Hydrometer is a large glass floating hydrometer which is hand-calibrated with tiny weights to achieve a very accurate reading of specific gravity. The measurement scale of the Dupla Marin Hydrometer is proportionally large as well allowing precise measurements of salinity to within 0.2 ppt – no swing arm hydrometer or analog refractometer can read anywhere close to that.
It may not be practical to use the Dupla Marin Hydrometer for an everyday salt testing tool, but instead its real calling may lie in serving as a reference tool for calibrating other hydrometers and refractometers. At a given temperature, probably 25C (~77F), the accuracy of the Dupla Marin Hydrometer should be about as high a level hobbyists could ever hope to achieve, allowing proper measurements of one of the most crucial parameters for life-supporting seawater in aquariums.
The kind of hand-crafted, hand-calibrated glass Hydrometer the likes of which Dupla Marin is offering won’t be cheap. Like PAR meters, the Dupla Marin Hydrometer is exactly the kind of seldom-used but high value equipment that an LFS or aquarium club could invest in for the benefit of their customers and club members.