The Essential Equipment for a Working Tank

A functioning aquarium needs five things: a tank, a filter, a heater (for most fish), lighting, and an air pump or water circulation method. You also need substrate (gravel or sand for the bottom), a water conditioner to remove chlorine, and a way to test water quality. Everything else—decorations, plants, special foods—comes after those basics are in place.

The tank itself should be at least 20 gallons for most beginner setups. Smaller tanks swing wildly in temperature and chemistry, making them harder to keep stable. A 20-gallon tank is roughly 24 inches long, 12 inches wide, and 16 inches tall. Glass tanks cost less than acrylic ones but are heavier and can crack if you move them. Acrylic tanks are lighter and won't shatter, but they scratch more easily.

Key Takeaways

  • A 20-gallon tank with a filter rated for that size is the practical minimum for keeping fish alive without constant water changes.
  • A heater is essential for tropical fish and most community tanks, and should be sized to raise the water temperature by 5 degrees Fahrenheit per hour.
  • A water test kit that measures ammonia, nitrite, nitrate, and pH tells you whether the tank is safe for fish or still cycling.
  • You need a water conditioner to remove chlorine before adding tap water, and a gravel vacuum to remove waste from the bottom during water changes.
  • The filter should process the entire tank volume at least three times per hour—a 20-gallon tank needs a filter rated for 60 gallons per hour or higher.

Choosing and Sizing a Filter

The filter is the most important piece of equipment after the tank itself. It removes waste, grows beneficial bacteria, and keeps water from becoming toxic. A filter rated for your tank size means it can move the water through the filter media at least three times per hour. For a 20-gallon tank, you need a filter rated for 60 gallons per hour (GPH) or more.

Three common types work for beginners: hang-on-back filters (HOB), canister filters, and sponge filters. Hang-on-back filters are cheapest and easiest to maintain—they clip to the rim of the tank and are straightforward to clean. Canister filters sit under the tank and hold more filter media, so they go longer between cleanings, but they cost more and are harder to set up. Sponge filters are the cheapest option and work well in smaller tanks or breeding tanks, but they need an air pump to run.

Heating and Temperature Control

Most fish kept in home aquariums come from warm water and need a heater to survive. Tropical fish typically need water between 75 and 80 degrees Fahrenheit. A heater should be sized so it can raise the water temperature by 5 degrees per hour. For a 20-gallon tank, a 200-watt heater is standard; for a 40-gallon tank, use 300 watts.

Submersible heaters are the most common type—they sit inside the tank and have a thermostat that turns them on and off automatically. Place the heater near the filter outlet so warm water circulates throughout the tank instead of creating hot spots. A thermometer (stick-on or floating) lets you check the temperature without opening the tank. Check it daily for the first week after you set up the tank.

Lighting and How Long to Run It

Fish need light to see and eat, and plants need light to grow. Most aquariums use LED lights because they use less electricity and produce less heat than older fluorescent bulbs. A basic LED strip that clips to the top of the tank costs between $20 and $50 and works for most setups.

Run the light for 8 to 10 hours per day. Longer than that can cause algae blooms; shorter than that can stress fish and prevent plants from growing. A straightforward plug-in timer (the kind used for lamps) lets you automate this without thinking about it. Place the light so it shines evenly across the tank and does not create harsh shadows.

Water Testing and Chemistry Basics

Before you add fish, you need to know whether your water is safe. A water test kit measures ammonia, nitrite, nitrate, and pH. Ammonia and nitrite should be zero; nitrate should be below 40 parts per million (ppm). pH should match the needs of the fish you plan to keep—most community fish do well between 6.5 and 7.5.

Liquid test kits (the kind where you add drops and watch the color change) are more accurate than test strips, though they take longer. A basic kit costs $20 to $30 and lasts for hundreds of tests. Test the water when you first set up the tank, then every few days for the first month, then once a week after that. If ammonia or nitrite is above zero, the tank is still cycling and is not ready for fish.

A water conditioner removes chlorine and chloramine from tap water so it does not harm fish or beneficial bacteria. Add it to the water before it goes into the tank. Most conditioners also bind heavy metals. Follow the bottle's instructions for how much to use based on the volume of water you are adding.

Substrate, Decorations, and Maintenance Tools

Substrate is the material on the bottom of the tank. Gravel and sand both work; gravel is easier to clean and less likely to compact, while sand looks more natural and is better for fish that like to dig. Use about 1 pound of substrate per gallon of water. Rinse gravel or sand thoroughly before adding it to the tank—tap water will turn cloudy otherwise.

Decorations (rocks, driftwood, plastic plants) give fish places to hide and explore. Live plants are optional but helpful because they consume nitrate and produce oxygen. Java fern and anubias are hardy plants that do not need special lighting or fertilizer.

You will need a gravel vacuum (a siphon with a wide tube) to remove waste from the bottom during water changes. A bucket for carrying water, a net for catching fish if needed, and a scraper for removing algae from the glass round out the basics. A water change schedule of 25 percent of the tank volume once per week keeps nitrate from building up.

Setting Up the Tank Step by Step

Start by placing the tank on a sturdy, level surface away from direct sunlight and heat sources. Add the substrate, then fill the tank halfway with tap water treated with conditioner. Place the filter, heater, and any decorations. Finish filling the tank with treated water.

Turn on the filter and heater and let them run for at least 24 hours before adding fish. Test the water daily. The tank is cycling—beneficial bacteria are growing on the filter media and substrate. This takes 2 to 4 weeks. Ammonia will spike first, then nitrite, then both will drop to zero and nitrate will appear. Only when ammonia and nitrite are both zero is the tank ready for fish.

Add fish slowly, a few at a time, over several weeks. Adding too many at once overwhelms the bacteria and causes ammonia spikes that kill fish. Start with hardy species like tetras, guppies, or corydoras catfish.

Frequently Asked Questions

Do I need an air pump if I have a filter?

Not always. Most hang-on-back and canister filters create enough water movement and surface agitation to add oxygen. Air pumps are useful if you want extra aeration, are running a sponge filter, or have a heavily stocked tank. They are cheap insurance and do not hurt.

Can I use tap water straight from the faucet?

No. Tap water contains chlorine and chloramine to make it safe for humans but toxic to fish and beneficial bacteria. Always treat tap water with a water conditioner before adding it to the tank. The conditioner neutralizes these chemicals in seconds.

How often do I need to change the water?

A 25 percent water change once per week is the standard for most tanks. If you have fewer fish or a larger tank, you may be able to go longer. If you have more fish or a smaller tank, you may need to change water twice per week. Test nitrate levels to guide your schedule—if it stays below 20 ppm, your schedule is working.

What if the tank gets too hot or too cold?

A heater prevents cold water. For heat, move the tank away from direct sunlight, make sure the room is not too warm, and may support the filter is running to circulate water. In extreme heat, some people float a bag of ice in the tank as a temporary fix, but this is not a long-term solution. A chiller is expensive and usually not needed for home aquariums.

Can I use a smaller tank to save money?

A 10-gallon tank costs less upfront but is harder to maintain. Temperature and chemistry swing wildly in small volumes, and a single mistake (overfeeding, a dead fish) can crash the whole system. A 20-gallon tank is only slightly more expensive and is much more forgiving for beginners.