June 13, 2014 at 1:00 am

Living

Do your homework before setting up an aquarium

Readying the environment is the key to safely caring for aquatic pets. (Chang W. Lee / New York Times)

Setting up an aquarium sounds simple enough, but there are a few decisions you need to make before diving into first-time fish ownership. Figure out the answers to questions like these before heading to the pet store:

Pick out a tank: Determine how much space you have and how big a tank you want. Take into account the type of fish you’re interested in, as some require more space than others. For example, cichlids and angelfish — colorful tropical varieties that catch the eye — can be aggressive and outgrow small tanks quickly.

Stephen Zawistowski, Ph.D., science adviser for the ASPCA, recommends starting with a 20-gallon freshwater tank, which will allow you to choose from a wide selection of fish without having the tank take over your entire living room. Plan for an inch of fish for every gallon of water.

Next, choose a location for the tank. It should be out of direct sunlight, away from vents, close to electrical outlets and a water source, and on a sturdy surface.

Stock up on supplies: Along with a tank, you’ll need a filter, possibly a heater (for tropical fish), a light (to provide day and night cycles), a dechlorinator (to neutralize chlorine and chloramine), a water-testing kit, gravel (about a pound for every gallon of water), a thermometer, and decor, such as plants. Skip the starter kit, which is often inadequate.

Prime the habitat: Give yourself a little lead time to prepare the tank. First, clean it with a baking-powder paste. Wash the gravel and decor and wipe the aquarium with a water-and-vinegar solution; then set the gravel and decor in the tank. Fill it with water, add the dechlorinator, and let it sit for up to a week. Called aging, this allows the chemicals in tap water to evaporate. (About once a week, replace 10 to 30 percent of the water in the tank with fresh aged water. After the initial setup, you’ll need to age the water in a separate container.)

Test the water: Next, you need to make sure the aquarium’s pH, nitrite and ammonia levels are OK. Some pet stores will test your water samples for free, or you can use an at-home kit. When the water’s ready, connect the filter and heater and let the tank run for at least 48 hours. Check the temperature: Water for warm-water fish should be between 78 and 82 degrees Fahrenheit; for cold-water fish, between 65 and 75 degrees. A heater will help maintain a constant temperature.

Finally ... buy your fish!: Once the water is ready, you can start to add fish. Begin with just one; a hardy type, such as platy, is a good starter. Put it in the tank, still inside the bag from the store, for 15 to 30 minutes. “This will help the water temperature between the bag and tank equalize, which is important, since temperature changes can kill fish,” says Don Spaeth, an aquatics expert in Greenville, Wis. Finally, set the fish free. Wait a week before adding a few more, and then continue adding weekly until your tank is stocked (remember: an inch of fish for every gallon of water).

Questions should be sent to Martha Stewart Living , 11 W. 42nd St., New York, NY 10036. You may also email questions to mslletters@marthastewart.com. Please include your name, address and daytime telephone number.