Freshwater Versus Saltwater Aquariums: What You Need to Know

6 min read

By Adam Denish, DVM

Perhaps you’ve wandered into the aquarium department of your local pet store and taken a good look at the faces of the fin-tailed. It’s easy to fall for the beautiful colors, the graceful movements and the soothing sounds of the water. If you feel like you’ve been hooked, read on to learn what decisions beginning fish hobbyists need to make when contemplating the details of adding a new aquarium to their home.

Freshwater or Saltwater?

Water covers about 75 percent of the Earth. In the assorted bodies of water, lifeforms have evolved to survive with varying amounts of dissolved salts and minerals, varying temperatures, oxygen levels and depths. When building an aquarium, you aim to recreate the conditions of the environment where the inhabitants have originated. The pet trade has broadly divided the aquarium habitats into freshwater (tropical) or saltwater (marine). A comparison of the components of these habitats will help new fish keepers make an informed decision about how to select an aquarium suitable for their lifestyle.

The Livestock

Both saltwater and freshwater aquariums feature an amazing cast of characters. In addition to fish, there are invertebrates like snails and crabs to make your tank more interesting. Freshwater tanks can include plants while saltwater tanks can include corals and anemones.

A beginning aquarist might opt for a community freshwater tank filled with guppies, mollies and tetras. It’s a good idea to add scavengers, like snails and cory cats, to a freshwater tank to help manage the build-up of algae. Alternatively, a tank of a single species such as fancy goldfish, discus, or angelfish makes a beautiful aquarium and allows the keeper to become very knowledgeable about the habits of their favorite fish. Freshwater fish can reproduce easily if the water quality, temperature and surface space exists so be prepared with a nursery tank. Aquascaping with live freshwater plants can add additional interest and serve as a wonderful hiding place and food source for the fish.

Saltwater fish are brightly colored and have fascinating habits. The watchman goby occupies a small cave-sized opening at the bottom of the tank, guarding its territory around the clock. Clownfish have symbiotic relationships with certain species of anemones. Pufferfish are friendly to their owners, often swimming to the front of the tank and “begging” for attention. Owners of saltwater aquariums undoubtedly grow attached to their fish and take pleasure in watching the interactions. Compatibility charts should be consulted when choosing tankmates, as fish come from a variety of seas where the species might not ordinarily meet.

A saltwater hobbyist must make the choice of building a fish-only tank or a reef system. While the saltwater fish are fascinating on their own, corals bring a new level to the hobby. Choosing a reef aquarium will determine the type of lighting required and add some additional water quality maintenance. Not all fish are compatible with corals so be sure to do your homework when choosing tank inhabitants.

The Water

The fish in freshwater aquariums have their origins in streams, ponds, rivers and lakes. The water for these fish should be dechlorinated, which can be accomplished by adding a dechlorinating agent to tap water. The water should also have movement to increase the amount of oxygen which can be achieved by using an air pump. Aquarists routinely monitor the temperature of the water to be sure it is stable and also test the levels of ammonia and pH to ensure that waste is properly removed by the filter. Always research the fish you purchase for any additional requirements for the water, as some fish (like koi) swim in colder water or prefer shall water depths (like archer fish, which hunt for insects).

Salt for marine aquariums is available to mix with home tap water to make a ratio comparable to seawater. A hydrometer measures the specific gravity of the water, indicating how salty it is. Some invertebrates, like corals and anemones, require specific additives like calcium and iodine to a saltwater aquarium. Similar to a freshwater set-up, monitors for temperature, ammonia levels and pH are needed.   

Related Posts

Top Three Pet Sharks

Vladimir Negron
Mar 22, 2016

Facts About Catfish

PetMD Editorial
Mar 23, 2017

10 Facts About Puffer Fish

Jessica Remitz
Oct 21, 2016