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Water and Water Quality

Marine aquariums can be filled with natural seawater or fresh water plus a synthetic seawater mix. Natural seawater contains numerous microscopic organisms, both plant (phytoplankton) and animal (zooplankton). If the water is not properly conditioned by dark storage for a few weeks, the death of these organisms could radically alter the chemistry of the water, endangering your aquarium specimens. Secondly, unconditioned water could transmit infectious diseases to your marine fish. Some aquarists prefer to collect their own water, but it is safer and more convenient to use a good quality synthetic sea salt mix. This is especially true for the new marine aquarist who will find the storage and filtering procedure bothersome and time-consuming.

If you do decide to collect your own seawater, it must be collected away from inshore areas that could be polluted from fertilizer runoff, sewage, heavy metals, insecticides, or other pollutants. Inshore waters also often contain large quantities of suspended particles. Collect seawater only in nontoxic plastic containers with good fitting caps. The water should be stored in closed plastic or glass containers for several weeks before use. After storage, you will note on the container bottoms a fine layer of sediment that should not be added to your aquarium. After addition to the aquarium, the water should be subjected to filtration and aeration for several hours before addition of fish. It is also recommended that several water tests be conducted, including pH, ammonia, nitrite, and nitrate to insure that they are within safe levels.

Synthetic Seawater

The major advantages of preparing synthetic sea water are that it is free of pollutants and micro-organisms that could transmit disease or foul the water, there is no need for storage of extra seawater, and the preparation can be used within a short time after mixing.

Various commercial mixes are available for making seawater. The salt is simply mixed with an appropriate amount of tap water, allowed to mix until thoroughly dissolved, and then the salinity adjusted to the acceptable level. Using this method, fish can be introduced to the new aquarium in as little as 24 hours. Although fish can generally be introduced earlier than 24 hours, some salts require linger to completely dissolve.

Conditioning Water

All municipal water should be treated with a good-quality water conditioner prior to mixing with sea salts. These conditioners are available as a liquid or powder. When used according to instructions, they will destroy chlorine and chloramines within minutes. Some conditioners will also render metallic ions nontoxic if they are present in your tap water. Some brands of synthetic sea salts contain a water conditioner that will destroy chlorine and chloramine while the sea salts are dissolved. Water conditioners should always be used whenever adding new tap water to the aquarium.

Specific Gravity and Salinity

The specific gravity (or density) if the ratio of the amount of total dissolved salts in water when compared to pure water. Pure water has a specific gravity of 1.000. As more salts are added to water, the specific gravity increases.

The amount of salt in a marine aquarium is determined by the use of a hydrometer. This instrument is made of a sealed glass tube with an internal scale. The hydrometer is weighed at the bottom and floats freely when placed in water. High quality scientific hydrometers are standardized against a sea water sample at a known temperature, usually 59° F (17° C). If a reading is taken at any temperature other than 59° F (17° C), the reading must be corrected using a table of correction factors. Such tables also give the salinity value. The temperature must be taken into account, since as water becomes warmer, it expands or becomes less dense

Water Chemistry

The pH of the water can be monitored by the use of inexpensive test kits. A few drops of an indicator chemical are added to a sample of aqarium water in a test vial. The color of the sample is compared to a color chart that indicates the pH of the water. This test should be run weekly for fully established aquariums, and every few days for new aquariums. A pH kit is essential for all marine aquarists.

Dissolved Oxygen

Aquatic marine animals in nature inhabit an environment with an abundance of dissolved oxygen. In aquariums equipped with proper filtration and aeration, sufficiency of dissolved oxygen is seldom a problem. It is therefore generally unnecessary to test oxygen in aquariums. However, it must be understood that the higher the temperature of the water, the less oxygen dissolves in the water.

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