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There are many differences between having a freshwater aquarium versus having a saltwater aquarium. These differences include how you initially set up the aquarium and all ongoing care, maintenance, everyday chores, and costs requirements. There are several key issues you will need to consider while you choose:  Saltwater aquariums cost more. Saltwater aquariums have specific water requirements that need extra tools and equipment to maintain it, as opposed to maintaining a freshwater aquarium. For example, most saltwater aquariums need protein skimmers or a foam fractionator in addition to the regular filter system that all aquariums need. Unlike a regular aquarium filter, protein skimmers completely remove dissolved organics from the water which is vitally important for saltwater aquariums where a buildup of nitrates can be deadly. Water changes are easier for freshwater tanks. All aquariums need weekly or bi-weekly partial water changes. For freshwater aquariums, simply doing a 10% to 20% water change with an aquarium vacuum and refilling the tank with dechlorinated tap or filtered water is enough. However, saltwater aquariums will require you to mix new saltwater days before your scheduled partial water change. There are more saltwater invertebrates and fish to choose from. In terms of aesthetic and choice, there are more options available if you are choosing to have a saltwater aquarium. You can find stunning saltwater fish like angelfish, clownfish, and lionfish and a vast array of invertebrates available like starfish, shrimps, worms, and corals. Saltwater fish may need special diets. In most cases, getting freshwater fish to eat flakes is not a problem. However, if you choose saltwater fish, especially those that need to be caught from the wild, they may need special diets or be weaned into eating conventional fish flakes and food. Giving fish an inadequate diet can lower their immune systems and cause diseases, which can eventually lead to death. A small fish tank set up is generally more economical than a large fish tank. There are several issues you should consider when choosing the size of your tank:  Where will you put your aquarium? The best place to put a fish tank is away from direct sunlight and heater vents. Fluctuations in temperature and sunlight can cause green algae to form and dirty the water quality of your tank. In some cases, the best location for an aquarium can restrict the size of your tank. Your aquarium stand should be able to withhold the weight of the tank. For each gallon (4 litres) of water, there is approximately 10 pounds (4.5 kilograms) of weight. Obviously, smaller tank would hold less weight than a larger one. It’s harder to maintain the quality of water in a small fish tank. This means you will need to do more partial water changes than if you had a large fish tank. The size of your tank will determine what type of fish you can have. Most fish require at least 5 gallons (20 litres) of water with the exception of betta fish that don’t need as much water. However, being able to survive in a certain condition doesn’t necessarily mean the fish is thriving or living a happy life. There are three main saltwater aquarium types: Fish Only, Fish Only with Live Rock (FOWLR), and the Reef Tank.   Fish Only Tanks: As the name suggests, this tank only houses saltwater fish. It is the least expensive way to set up a saltwater aquarium. However, it does have its disadvantages. Fish Only tanks take longer to set up, require more frequent tank maintenance and testing, and have a shorter shelf life than the other types of saltwater aquariums.  Fish Only with Live Rock: FOWLR tanks are set up like Fish Only tanks but with the addition of live rock and better aquarium lighting. The live rock acts as a natural biological filter for saltwater and keeps your tank healthier than a Fish Only tank. A live rock has hundreds of tiny creatures and biological organisms living inside and on the surface of the rock.  Reef Tank: If you choose this type of saltwater aquarium, you are most likely looking towards having invertebrates, corals, or anemones as the main focus of your aquarium and fish are just an afterthought. Reef tanks require daily water quality checks, high lighting levels, extra water supplements, heavy duty filtration systems and are generally the most expensive to maintain. Reef Tanks are recommended for more experienced aquarium hobbyists. The kind of lighting and the temperature of your aquarium depend on what kind of aquarium you have and who your tank inhabitants are. The type of light you choose also affects the overall temperature of your tank.   Aquariums that are Fish Only: This means your freshwater tank will not have real or live plants in it. In this case, you will most likely be using fluorescent lights that are between 18 and 40 watts.  Freshwater aquariums with plants: The type of lighting you’ll need will depend on the depth of your tank, the plant species you have, and the desired growth rate of the plant. Usually, you should provide 2 to 5 watts of light per gallon in a planted freshwater aquarium. Always research and consult with your aquarium expert when you plan to have plants in your tank.   Saltwater Reef Tanks: These tanks need high levels of light that are characteristic of high output fluorescent and metal halide lamps. Some corals may even need more intense levels of light that can be achieved with T5-HO, Very High Output (VHO), and metal halide lights. All filters have three functions to them, which include mechanically filtering the water by trapping or removing free floating particles, biologically filtering the water by growing good bacteria, and chemically filtering the water by dissolving wastes. There are various types of filter:   Mechanical Filter: The most popular type of filter is the corner filter that recycles water through the three-filtration stages. It usually sits at the top of the aquarium in the middle or in the corner and sucks up water through a tube and spits it out again.  Undergravel Filter: This filter provides good mechanical filtration since it is located underneath the gravel in plates, which forces the water to filter through the rocks, trapping and taking any fallen particles in the water.  Canister Filter: This high end filtration system operates by having multiple trays that mechanically, biologically, and chemically filter the water. It filters the water by pushing water from the bottom of the canister to the top.  Protein Skimmer: This filter is necessary if you have a saltwater aquarium. Protein skimmers remove dissolved organic materials from the water as opposed to other filtration systems that only trap it until you change the filter.
Decide if you want a freshwater aquarium or saltwater aquarium. Think about the size of tank you’d like. Choose what type of saltwater aquarium you’d like to set up. Determine what the correct lighting and heating for your fish is. Choose the appropriate type of filter or filters for your tank.