Coral - January/February 2010

Do you want a
Veggie Clip
that doesn’t
Suck

Two Little Fishies VeggieMag doesn’t need a suction cup because it’s held in place by powerful neodymium magnets.

Position it at any level in the aquarium, and retrieve it without getting your hands wet.

What’s more, it floats, so it won’t get lost in the aquarium.

TM

tested, in order to avoid inaccurate measurements.

Refractometers range in price, but offer a high degree of precision if kept calibrated

Refractometers: Finally, there are refractometers and meters for measuring electrical conductivity, which are increasingly being used to determine density in the marine aquarium hobby.

A refractometer works on the principle that light changes direction (is refracted) on passing through an air/ water interface. The angle of refraction is dependent on the temperature and the concentration of dissolved salts. A refractometer measures the angle of refraction and uses this to indicate the density on a scale. Before it is used, the refractometer must first be calibrated using de-ionized water or a calibrating solution of known salinity, and then the specific gravity of a sample can be determined. As with a hydrometer, the density measurement will be temperature-dependent.

WHICH DENSITY METER
IS BEST?

Electrical conductivity meters and refractometers may produce the most precise measurements, but both are expensive, and the majority of beginners in the marine aquarium hobby are very prone to making errors when using them. I recommend that the novice buy a good-quality glass hydrometer or swing-arm box unit. One of these two reasonably priced density meters should be part of the standard equipment of every marine aquarium, and their accuracy is quite adequate.

One final tip in conclusion: if you are worried that something is amiss with the density of your water, you should check it with a meter of another type and from another manufacturer. If, for example, the reading was taken using a glass hydrometer, then check it against the reading from a swing-arm unit. Alternatively, you can check the functionality of the density meter by measuring the density of the water of an aquarium known to be in good order.

REFERENCES

Patent-pending design by Julian Sprung for: Two Little Fishies Inc. www.twolittlefishies.com

Conductivity meters: Sea water conducts electrical current—the more salts are dissolved in the water and the higher its temperature, the better. This flow of electricity can be determined using electrodes, and in the case of sea water, is measured in millisiemens per cm (mS/cm). With the aid of appropriate tables, the conductivity can be converted to salinity or density (see, for example, Fosså & Nilsen 2001). A density of 1.023 g/ml (salinity 34. 7 percent at 77°F [ 25°C]) corresponds to a conductivity of around 52. 5 mS/ cm. When using conductivity meters, correct calibration and the use of top-quality electrodes are important; the latter should be regularly cleaned and, if necessary, replaced.