A saltwater aquarium can be home to a wide variety of aquatic organisms: fish, crustaceans, even invertebrates such as coral, anemones and sea stars. Many people think if you have salt and water in an aquarium, you have a saltwater aquarium. Unfortunately, setting up and maintaining a saltwater aquarium is a little more complex than than that. A healthy tank must not only support the fish but also feed the bottom-dwelling invertebrates.
Salt is the first thing people think about when setting up a saltwater aquarium, and it is true that the saline level is important to create a healthy tank. Salinity of water is measured in specific gravity. Specific gravity is a scale that measure the density of fluid. Distilled water has a specific gravity of 1. Seawater is denser with many more dissolved chemicals, so it has a higher specific gravity. While the specific gravity of the ocean varies depending on the area, but it generally stays between a specific gravity of 1.018 and 1.025. This translates roughly to 24.6 to 32.7 grams of salt per liter of water.
The salinity of a tank is tested with a hydrometer. Place a drop of water on the glass slide of the hydrometer and look through the eyepiece. A scale on the side of the viewer shows the level of salt present in the drop of water.
Fish and all marine creatures are sensitive to pH levels, which is a measure of the acidity and alkalinity level of a substance. The pH scale ranges from 0 to 14. A balanced pH level is 7. The lower the pH level, the more acidic the water. A higher number indicates base water. Fish require a basic environment. Healthy water for fish should have a pH level between 8.0 and 8.4.
There are a wide variety of pH test kits available, but they all work in a similar way. You place a water sample in a clean plastic tube. Then add three drops of test solution to the water and place a lid on the container. Shake the container and compare the color of the sample with the color key provided with the test. Test kits come with acid and base solutions that can be added to the water supply to create the ideal pH.
Nitrates are the by-products of decomposition. As plant materials and waste products decompose, the nitrogen they contain is released into the water. Unless the aquarium contains nitrogen-absorbing plants, the nitrogen molecules bind with the oxygen forming nitrates. This not only removes oxygen that the fish need, but the nitrates stress the fish. In extreme cases, the nitrates build up and form nitric acid, which changes the pH of the water. A saltwater tank should remain under 20 parts per million of nitrates.
Nitrate testing kits are inexpensive and easy to use. They are similar to the pH testing kits. A nitrate test solution is added to the sample and the color is recorded. If high nitrates develop, the water must be changed.
Saltwater aquariums with a live reef require enough calcium in the water to nourish the reef. A healthy reef aquarium should have between 400 and 450 parts per million of calcium. There are a wide variety of calcium test kits that change color when a test solution is added to a water sample. Because calcium is heavier, the water sample should be taken from water near the bottom of the tank.