The Dupla Marin high resolution Hydrometer came along at a time when we are really becoming quite critical about salinity measurement. This large, oversize hydrometer is specially designed to measure seawater salinity at 25C/77F but only between 33 and 38 parts per thousand.
Dupla Marin’s new hydrometer absolutely dwarfs our 20 year old Marine Enterprises hydrometer with a specific gravity measurement scale that is practically as long as the entire TME piece of glass. But that same scale can read specific gravity to within 0.0001 which translates to a salinity resolution within 0.0002 grams per milliliter of seawater.
The one drawback of having such a large nearly 15 inch long hydrometer is that it is not exactly practical to use in the aquarium. Furthermore, Dupla Marin shipped the Precision Hydrometer with an 18 inch tall beaker that requires two cups of water to fill for accurate measurement of seawater. The one thing that Dupla Marin’s giant hydrometer does not include is a thermometer so you’ll have to bring your own, and to make sure that the temperature of the hydrometer equilibrates with the water to be tested before making a measurement you can count on.
As you might imagine, the Precision Hydrometer from Dupla Marin is not our everyday measuring device but instead serves as our very own hardware salinity reference device for calibrating our stable of various refractometers. Refractometers can be made for measuring saltwater or seawater, and calibrated for use in 20 or 25 Celsius, that’s a range from 68F to 77F leading to lots of potential errors in measuring the precise level of salt in our aquariums.
In addition to serving as the salinity standard for our fish room, the other very applicable scenario wherein the Dupla Marin Hydrometer really proves its worth is when making up new seawater for changing on the aquariums. With its high precision and high resolution, the Dupla Marin Hydrometer can measure tiny differences in the amounts of salt concentrations.
In 50 gallons of seawater at 35 ppt, there is approximately 14.57 pounds of salts in solution but at 33 ppt there is only 13.75 pounds of salts. We are lucky to get within 2 parts per thousand when measuring salinity with our basic $50 refractometers, assuming they are accurately calibrated. With a difference of just 2ppt you are talking about almost a discrepancy of a pound of salts in a 50 gallon volume of seawater with a difference between 33 and 35 ppt – that’s a lot of salt, and calcium and alkalinity.
Some reefers get caught in an endless cycle of chasing the calcium&alkalinity dragon’s tail, always trying to hit very specific or elevated calcium and alkalinity levels when all they really need to do is get serious about measuring salinity, and simply add more salt to their seawater mix. Considering salinity level is one of the most important parameters for keeping a reef tank, using a device like the precision hydrometer by Dupla Marin is a very worthy investment.
The Dupla Marin Precision hydrometer is not yet available in the US through any distribution channels but it retails in Europe for around $60 to $80 and if we hadn’t already received this sample for review, with our ever growing criticality about measuring salinity in our aquarium we wouldn’t hesitate to pay twice that to have a simple reliable device to tell us how much salt is actually in our fish and coral tanks.
FTC regulations require that we inform you that we were given this product for review, but our opinion of a product is never affected by how we acquire them.