Salinity is extremely important for marine ornamental fish. What is meaningful to fish is that a change in salinity means a change in osmotic pressure. For most coral reef fish, the salinity range that can be tolerated is less than 2‰. Sudden large-scale changes in salinity are often one of the reasons for the death of this fish.

There are two options for using sea water. The first is natural seawater, and the second is artificial seawater. The use of natural seawater is good, and it can meet the daily needs of seawater ornamental fish. But this method is only suitable for people on the beach. And because it comes from nature, it will inevitably bring many unfavorable factors. For example, various germs and bacteria that naturally exist in seawater, and various pollutants caused by human activities. Once they enter the aquarium, they are difficult to remove, so they must be cleaned before using natural sea water. Artificial seawater is artificially prepared after analyzing seawater. The advantage is that it is convenient and reliable, and it will avoid the harm of many bacteria.