If you’re thinking about setting up a fish tank in your home, there are a number of choices you need to make. First, what kind of fish do you wish to keep? Different kinds of fish require different care, different conditions, different equipment, and other variables.

If you’re just starting out, there are many reasons to begin with a freshwater tank versus a saltwater tank. To begin with, freshwater tanks are much cheaper -- equipment, supplies, and the fish themselves. Fresh water is easier to maintain; if you make mistakes, freshwater tanks give you a much broader margin of error. And repairing any mistakes are less costly as well. Also, because of this cheap cost, if you decide that keeping fish is not for you, your initial investment will not have been too burdensome.

Saltwater aquariums are more complex and more expensive to set up and maintain, but saltwater fish are generally more colorful, more interesting, and more fun to look at. A saltwater aquarium is a more complete environment; a saltwater reef tank, for instance, will often have thousands of organisms to look at. You will have an entire ecosystem in your living room, which will be not only attractive but also educational. Not only will you have colorful coral in your saltwater reef tank, but you can also add snails, shrimp, and crabs, which will add further interest to your tank and will also serve to clean the tank.

If you’re still not sure, you can always start out with a freshwater system, and then convert to salt water as you learn more about keeping fish.

If you start with fresh water and have the space for it, go for a bigger tank; large tanks are more stable in terms of water chemistry and temperature, and are thus easier to maintain. Conditions will change more gradually, and thus it will be easier to correct any mistakes. A good size to start with might be a 3-foot-long tank that holds 20-25 gallons of water.

Your dealer will help you with all the equipment you’ll need, but generally you will have to purchase a tank, a filter, a heater, a lid with lighting, some kind of substrate (gravel or sand), and other decor (rocks, pieces of wood, and plants, whether live or plastic).

Positioning your tank is also important. Make sure that the furniture holding your tank is solid; water weighs 8.35 pounds per gallon, so a 25-gallon tank would weigh more than 200 pounds, plus the weight of the tank itself and all the equipment. Try to position the tank away from direct sunlight (which would encourage the growth of algae), and away from locations where it might be difficult to maintain a stable temperature (such as near a radiator or open window with drafts). A quiet location is better than a high-traffic area.

After the tank, the filter system is the second most important component of a freshwater aquarium. Filters eliminate both physical and chemical waste, and aerate the water; for effective system maintenance, your filtration system should filter all the water in the tank at least four times an hour. There are a variety of different filters on the market; make sure that your filter is powerful enough for the size of your tank.

Canister filters are the most powerful filtration systems; they are suitable for medium-sized to large tanks, and are mounted outside the tank. Canister filters force the water through, rather than allowing water to flow through gradually. Power filters are perhaps the most commonly used; they hang off the back of the aquarium, are easy to install and maintain, and provide both mechanical and chemical filtration. Another type of filter is a UGF, or under-gravel filter, which is positioned inside the tank under the substrate. Although inexpensive and easy to maintain, UGFs tend to clog, and are not a good choice if your tank includes live plants.

Your freshwater aquarium will also require a heater; there are several types of heaters, but be sure you select one with a thermostat. Selecting the proper heater is a matter of determining the average room temperature and the water temperature you wish to maintain, and then calculating the wattage you will require to maintain that water temperature for the size of tank that you have. For instance, if your average room temperature is 68 degrees Fahrenheit and your desired water temperature is 75 degrees, you will need to heat the water by 7 degrees on an ongoing basis. According to charts that are available online (and that should be available at your pet store), heating the water in a 25-gallon tank by 7 degrees requires 75 watts of power.

The best place to locate your heater is near where water is flowing, such as near the inflow or outtake of your filter. This way, the heated water is dispersed throughout the tank more quickly and more evenly.

Finally, you will need to determine what kind of substrate you wish to install in the bottom of your tank. For a freshwater tank, 2 or 3 inches of gravel lining the bottom of your tank is usually a good choice.

Once you get started with your freshwater aquarium, there are several other decisions you’ll need to make regarding design elements, lighting, and other issues, but with the above mechanics taken care of, you’ll be well on your way.