Hanna Instruments digital refractometer for salinity and specific gravity of seawater, one model.
HI96822
This Hanna Instruments digital refractometer measures salinity and specific gravity of seawater.
Marine organisms tolerate a narrow salinity band, and in a closed system salinity only rises, because water evaporates and salt does not. Topping up with fresh water is a daily judgement that should be made on a number.
Light bends by a different amount depending on how much is dissolved in a liquid. A refractometer measures that bend and converts it to a concentration scale. It needs one or two drops, gives an answer in seconds, and has no reagents and nothing to consume.
A digital instrument compensates for temperature automatically, which is the difference that matters: refractive index shifts with temperature enough that an uncompensated reading in a warm room is simply wrong.
Specific gravity readings are meaningless without their reference temperature; a digital instrument compensating automatically avoids the most common mistake in the hobby.
Supplied as one model.