April Arment's four-year-old son watches transfixed as the yellow and red tails of fancy guppies flare out like a fan. Suddenly, a flash of silver appears in the form of a white cloud tetra. He's not at the zoo or an exotic underwater theme park, but enjoying the aquarium in his bedroom in Landisville, Pennsylvania.

Fish fascinate kids and caring for one (or more!) teaches them responsibility. But while choosing and filling an aquarium isn't difficult, it involves more than throwing a few goldfish in a bowl. Here's what you need to know about what's involved.

The Tank
A larger tank is actually a better choice for beginners than smaller versions because larger volumes of water provide a more stable environment. "The fish won't pollute the water as fast and any chemical imbalances will affect the water less dramatically," says zoologist John Tullock, author of Bring Me Home! Saltwater Aquariums Make a Great Hobby.

A 10-gallon tank ($100 to $120) is most popular at That Fish Place/That Pet Place in Lancaster, Pennsylvania. However, if you can afford it, the 20 to 50 gallon tanks ($200 to $300) are ideal, says Matt Tartaglio, the store's aquarium installation manager. The one thing to avoid purchasing: a fish bowl, says Tartaglio, since they're easily affected by chemical imbalances or poor maintenance. They also tend to be home to goldfish, which are notoriously "messy" fish.

When it comes to what your tank should be made of, you have your choice of glass or acrylic. The main difference: glass tanks are less expensive and more durable than acrylic, but heavier; acrylic tanks are clearer, but they scratch easier than glass. As for the saltwater-versus-freshwater debate, a good bet for first-timers is to start with the latter. They're easier to handle because freshwater fish tolerate environmental variations better than saltwater fish.

Choosing Fish
Opt for small, hardy fish that don't produce a lot of waste. Tullock recommends guppies, swordtails and platies, while Tartaglio suggests fish in the tetra family, such as zebradanio, gourami and cory cats. Avoid goldfish, which produce a lot of waste and grow large - to about 12-inches long. Also, make sure not to overcrowd your tank. A good rule of thumb is a gallon of water for every inch of fish, says Tullock. That would be a maximum of 10 three-inch fish in a 30-gallon aquarium.

Turtles
If turtles are more your child's speed, consider getting a pond slider, painted turtle, map turtle or a musk turtle, says Tom Vargo, a supervisor at That Fish Place/That Pet Place. You can keep more than one turtle in a 20-gallon or larger tank, but only one in a 10-gallon tank, as they require a lot of room. Turtles are carnivorous, so you can't keep them with fish.

Supplies/Decorations
In addition to a tank, you'll need other supplies to set up your aquarium. Here's a checklist:

• A filter: Get one that is more than adequate for your tank size.
• Aquarium heater and thermometer (for tropical fish).
• Water chemistry test kit: For all the important water parameters: PH, ammonia, nitrite and nitrate.
• Tap conditioner: To remove chemicals such as chlorine (if you're using tap water).
• Gravel.
• Gravel siphon: To perform partial water changes. This tube takes water out of the tank and vacuums the dirt out of the gravel bed.
• A small net: For removing fish or dropped items from the tank.
• Decorations: For a natural look, choose rocks, driftwood and plastic plants. "Avoid using decorations collected outside because they haven't been treated for an aquarium," says Tullock. Alternatively, you can create a theme using plastic ornaments such as divers, sunken ships, castles, etc. Purchasing a background is another option, such as a plastic-coated underwater aquarium scene.

Care and Feeding
When you initially fill the tank with water, allow 24 hours for beneficial bacteria (that break down toxic substances from fish waste) to form, says Tartaglio. Then place one or two "starter fish" (the most hardy fish) in the tank. Wait a month before adding more fish to allow time for the filter to adjust to waste created by already-existing fish.

Once the tank is set up, change about 10 per cent of the water each week, says Tullock. You'll need to use a chemical to remove the chlorine from the tap water, clean the filter pads every two weeks and change them once a month after that.

When it comes to feeding fish, they only need a pinch or two of food every day. If you have more than one child taking care of the fish, Tartaglio suggests giving each one assigned days to care for them to avoid overfeeding.

Solving Problems
Be on the lookout for these common aquarium-related problems:

• Ich: Among other diseases, this parasitic disease appears as little white dots on the fish. This happens when the fish becomes stressed, either because the water chemistry is off due to poor maintenance, or because the power in the aquarium goes off. You'll need to get a tank additive from the pet store to kill the parasite.
• Cloudy water: This isn't necessarily a problem, especially if you are initially setting up the tank. If it's persistent over the long-term, however, it may be linked to a filtration system failure, says Tullock. You may need to invest in a new one.
• Excess algae growth: Green tank water is caused by a buildup of extra organics, the result of overfeeding, improper maintenance or leaving the aquarium lights on for 24 hours. Scrub the tank with an algae pad and the ornaments with a soft toothbrush then use the gravel siphon to suck out the excess.