Published February 10, 2013
It is a common belief among aquarists that freshwater tanks are easier to maintain than saltwater tanks. One of the main reasons cited for this belief is the fact that, in a saltwater aquarium, salinity must remain constant. While you must maintain proper water quality and chemistry in a freshwater tank as well, the added challenge of maintaining a stable salinity in a saltwater tank is more than some aquarium hobbyists feel fit to handle. It takes time for aquarists to get used to the routine of mixing and testing saltwater but, with the proper education, it does not need to be a difficult task – eventually it will become just another part of maintaining your aquarium.
The Importance of Salinity
As opposed to the majority of freshwater fish which are bred and raised on fish farms, many saltwater fish that are sold for the aquarium hobby are wild caught. During the first few months of captivity, it is especially important to mimic the natural environment of the ocean in all aspects of the saltwater aquarium for wild-caught fish. Saltwater tank salinity is only one major factor that can contribute to increased stress in newly caught saltwater fish - other factors
include levels of dissolved oxygen, the space limitations of a glass aquarium, and conflicts that may arise from cohabitation with other species. Experienced aquarists know that stress, perhaps more than any other factor, plays a large role in the health of your fish. If the salinity in your aquarium is not adequate or constant, your fish may become stressed and, as a result, they may fall sick and might fail to flourish.
What is Saltwater Aquarium Salinity?
Salinity, in plain terms, is the concentration of salt in aquarium water. More specifically, salinity is a measure of the dissolved sodium ions in the water and it can be measured in parts per thousand (ppt). Most saltwater aquarists measure the salinity in their aquarium using a hydrometer which measures the specific gravity in the tank. Specific gravity in a saltwater aquarium is the ratio of saltwater to pure water and it is easier and less expensive to measure than the actual salinity because special equipment is required to measure saltwater salinity in ppt.
How Salinity is Measured
Specific gravity is directly related to water temperature so, depending on the temperature of your tank, you may need to convert the results given by your hydrometer. Most hydrometers are calibrated at a temperature of 60°F and, since average aquarium temperatures lie between 75°F and 79°F, it is necessary to convert the results by adding 0.002 to the hydrometer reading. To get the most accurate reading, check the package your hydrometer came in to see what temperature the device was calibrated at.
Example: If your hydrometer is calibrated at 60°F and gives a reading of 1.020 and the temperature of your saltwater aquarium is 76°F then you must add 0.002 to the measurement which leaves you with a specific gravity reading of 1.022.
Unfortunately, many aquarium hobbyists have trouble maintaining a stable salinity in their tanks due to inaccurate specific gravity measurements. Inexpensive hydrometers are not always reliable and may give you an inaccurate reading. Another option for measuring the salinity in your tank is to use a refractometer. A refractometer is a device calibrated with pure water and it utilizes the index of refraction to give you a reading of your tank water’s specific gravity. All you have to do is place a few drops of aquarium water in the designation space on the device and close the cover. The device works by passing light through a prism that bends as it slows, making a scale visible by looking through an eye piece. These devices provide a measure of both salinity and specific gravity so they are a great tool for the saltwater aquarium hobbyist
The normal specific gravity range in saltwater aquarium
is 1.012 to 1.024. Any reading within this range is adequate, but keep in mind that it is imperative that you maintain a stable level of salinity within your aquarium. Thus, once you set up your aquarium and take a salinity reading, if you find that the specific gravity level is 1.023 you should try to maintain that level as closely as possible. There are several things which can contribute to saltwater aquarium salinity fluctuations, but the main factor is evaporation - as water evaporates from the tank, the salt is left behind so the salinity in the tank increases. By taking frequent specific gravity measurements you can keep the salinity level in your tank as close to constant as possible. It is also a good idea to keep a constant supply of premixed saltwater
on hand so you can refill your tank as necessary to accommodate for evaporation. Some saltwater aquarium hobbyists install a sump system
for their aquarium which not only houses their tank equipment but also increases the water volume of the tank, thus combatting evaporation.
With the proper equipment and regular water tests, it should be easy to maintain a constant level of salinity in your saltwater aquarium. If you take the proper precautions, you can make sure that the environment in your tank is as close to the natural environment of the ocean as possible. If you are successful you will be rewarded by the health and vitality of your thriving saltwater fish.