Caring for marine angelfish is often thought to be difficult and only to be attempted by the experienced aquarium owner. With the proper conditions, however, many of these fish can be quite hardy and live for many years. Their beautiful bright colors can make a focal point in a reef aquarium, which is appropriate because many angelfish are very territorial and will not easily share space with others of the same species. It is also important to be familiar with specific characteristics of the type of angelfish being purchased, as their food preferences, mature size, and habitat requirements vary considerably. When introducing new fish to a marine aquarium, special care should also be taken to properly acclimate them.
As with all marine species of fish, whose natural habitat is the ocean, saltwater angelfish can be kept only in a reef or saltwater aquarium. Starting a new aquarium for marine angelfish begins by using the proper type of water. Most tap water contains chlorine and other chemicals that can kill fish in high enough concentrations, and different fish are more or less sensitive to these substances. Devices and chemical additives can be purchased that will remove harmful agents from the water. Different species of saltwater angelfish may need different levels of salinity, alkalinity, or nutrient levels in the water to survive.
Another important factor in caring for marine angelfish is the water temperature. Unlike many freshwater species, many saltwater fish are unable to survive sudden fluctuations, and care must be taken to maintain a constant water temperature. Saltwater aquariums should have accurate thermometers and should not be placed near windows, heating and cooling vents, or other areas of the home where significant temperature changes are likely to occur. As with water content, marine angelfish may have differing needs for temperature depending on their natural habitat.
Many fish are sold as juveniles, so an inexperienced aquarium owner may not realize that a marine angelfish can need a lot of space when it reaches mature size, which can sometimes be more than 12 inches (30.48 cm) in length. It is often suggested that the minimum size for a saltwater aquarium is 72 gallons, which can be a significant investment, and that marine fish often need more space than their freshwater counterparts. In addition, some marine angelfish are often very territorial and may bite or even kill other residents of the aquarium, so it is important to know whether a particular type will need to be kept by itself or can coexist with other fish.