Converting your freshwater aquarium to salt water made easy

Posted by Brittany Griffiths on

Converting A Freshwater Aquarium To Saltwater can be simple. I have put together a basic step by step guide below to get you started 😊

A common misconception is that you have to have a degree to convert from freshwater to saltwater. This is of course not true, as a freshwater aquarium can be as challenging as a reef set-up, or as easy.

Knowledge is once again the key to a successful start and the more information you have the more fun you will get out of the hobby.

Another fairy tale is that saltwater requires a larger tank than freshwater. This is not so, a larger aquarium is generally easier to maintain than a small tank. Just picture nature as the ultimate Eco system. Any aquarium you set up is a copy and the smaller the copy the more difficult it gets to maintain and to provide a healthy and balanced environment.

Saltwater aquariums do not have to be expensive either. Despite the fact that most saltwater species are on the more expensive side, it does not imply that you can’t start out with “cheaper” fish.

The more you get into additional equipment the more expensive it gets, but the same applies to a freshwater aquarium.

Freshwater and saltwater, including live rock, can be compared by size and cost. The exemption is a reef set-up, where the lighting system alone can easily cost as much as a fish only tank.

The Aquarium

The tank itself can be used as is. There are no special aquariums that differ in fresh or saltwater set-ups. It is advisable to clean the tank with a sponge using water only. Household chemicals do contain substances that are detrimental to the aquarium.


The original filtration can be used in the new saltwater aquarium as well. Later on in time, especially if live rock and more animals are added, a change in filter type might be justified. In this case a Hang on the back or a protein skimmer can be added.

Biological Filtration

The nitrifying bacteria in fresh and salt water are closely related, but slightly different. The freshwater bacteria are good for spiking a brackish tank, but a different strain of bacteria needs to colonize saltwater aquariums. We sell live bacteria suitable for starting a marine aquarium !!. Seeding aquariums with freshwater bacteria will speed up the process of cycling the new saltwater tank nonetheless.

Pumps, Tubing, Heater

The tubing, heater, and air pumps from the freshwater tank can be used in the new saltwater tank. If cleaning is needed, water only is the way to go.


Plastic plants and décor should not be used in a saltwater tank. Most saltwater fish nibble on everything they can get a hold on. The new decoration can include live rock, rocks, or fake corals in the beginning.


The substrate for saltwater should either be sand, crushed corals, or aragonite. The substrate in saltwater not only provides biological filtration as in freshwater, but also as a home for many animals that might be added over time.

Coral Sand and aragonite will keep the pH stable as well as provide calcium for a later update to a reef system.

Should coral sand have been used in the freshwater set-up, it can be used for the saltwater tank ( eg: concerting from a African cichlid tank ).


At this early stage the regular fluorescent light will be fine. To enhance the color of the fish, one might be replaced with an actinic bulb. Lighting will get more important with a reef tank later on if desired.

Test Kits

Most test kits on the Australian market are both freshwater and saltwater compatiable. Please check the box for info.

General Notes:

In addition to the above, a good quality artificial marine salt or the use of natural sea water and a hydrometer to measure salinity will be required. For the first batch of saltwater, fresh water should be used instead of just mixing salt into the tank. The maintenance schedule for cleaning the tank and water changes remains the same as in freshwater.

For most tanks, all there is to it is to replace the gravel, remove and replace the décor and to add water with the seawater mix.

Most of the additives can be used as well, such as a water conditioner , stability etc.

Some additives are specifically made for saltwater, so check the labels on the packaging before using them.

After the conversion, the tank will still cycle. But if the existing filtration, with the bacteria cultures in tact, was used, the tank will complete cycling much faster then a new set-up.

Thanks for reading - Ben Aquarium Universe

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