Your First Aquarium: What to Buy and How to Set It Up

The Shopping List, in Order

1. Tank and stand. A 20-gallon (75-liter) or larger tank is far more forgiving than anything smaller.
2. Filter rated for at least the tank's real volume.
3. Heater, for tropical fish only.
4. Liquid test kit and water conditioner.
5. Thermometer, substrate and some decor for cover.
6. A lid, to cut evaporation and stop jumpers.

Why Bigger Is Easier

More water dilutes waste and steadies temperature, which gives you time to notice and fix a mistake. A small 5- to 10-gallon (19- to 38-liter) tank punishes overfeeding or a missed water change much faster: the opposite of what most beginners expect when they pick the smallest tank to save money or space.

Gallon sizes on tanks are usually US gallons. A UK gallon is about 20% bigger, which is why we give liters too.

Filter, Heater and Test Kit

Filter: choose one rated for at least your tank's volume; don't round down. A hang-on-back filter suits most beginner tanks, and a sponge filter suits small tanks or baby fish. Once the tank has cycled, the filter must run all the time, because it houses the bacteria that keep the water safe. See filters and pumps.

Heater: essential for tropical fish, because room temperature can drop at night. Goldfish and other coldwater fish don't need one. Heater sizing explains the wattage.

Testing and conditioner: a liquid test kit gives more reliable readings than strips while the tank is new, and conditioner makes tap water safe at every fill and water change. See water care and testing.

Choosing the Spot

Water is heavy: a liter weighs a kilogram, so a 20-gallon (75-liter) tank holds about 165 lb (75 kg) of water before you add the glass, gravel and rock. Use a sturdy, level stand made for aquariums, on a solid floor.

• Out of direct sun, which feeds algae and swings the temperature.
• Away from radiators, heating vents and air conditioners.
• Near a power outlet, with a drip loop in each cable so water can't run into the socket.
• Somewhere you can reach for water changes, and not where a door or a child's game will knock it.

Setup Day, Step by Step

1. Rinse the gravel or sand in a bucket until the water runs mostly clear. Most aquarium soils go in dry, so check the bag first.
2. Add the substrate in an even layer.
3. Fit the filter and heater, but leave them unplugged: a heater run dry can crack.
4. Arrange rock, wood and plants, leaving open swimming space.
5. Fill slowly, pouring onto a plate so the substrate isn't disturbed, and add conditioner as the label directs.
6. Plug in and wait 24 hours. Check the thermometer holds steady and let any cloudiness settle.

Then Cycle the Tank

Cycling grows the bacteria that turn fish waste into less harmful compounds, and it takes weeks, not days. Adding fish before it is finished causes more early losses than any other mistake. Cycling a tank explains how, and how to test when it is done. Then add a few fish at a time; community tropical tanks helps you choose.