What a tank is and why you build one instead of buying pre-made

Building a tank means assembling an aquarium from separate components—a glass or acrylic box, a stand, filtration system, heater, lighting, and substrate—rather than purchasing a complete kit. People build tanks because they can choose exactly what size, shape, and equipment they want, often at lower total cost than a finished product. You also gain control over water quality from the start, which matters if you plan to keep fish that need specific conditions.

The basic decision is between glass and acrylic. Glass is cheaper, scratch-resistant, and stays clear longer. Acrylic is lighter, less likely to shatter, and easier to drill for plumbing, but it scratches more easily and costs more upfront. For a first tank, glass is usually the practical choice.

Key Takeaways

  • A basic tank build requires a container, stand, filter, heater, lighting, and substrate—each chosen based on what fish or plants you want to keep.
  • Tank size matters more than shape; a 20-gallon long tank gives fish more room to swim than a tall tank of the same volume.
  • Filtration must handle the bioload of your fish; a filter rated for 2 to 3 times your tank volume per hour is a standard starting point.
  • You will need to cycle the tank—let beneficial bacteria establish—before adding fish, which takes two to four weeks.
  • The stand must support the weight of water (8.3 pounds per gallon), gravel, and equipment without flexing or tipping.

Choosing tank size and material

Tank size is the first real choice. A 10-gallon tank is the smallest that works for most fish; smaller tanks swing in temperature and chemistry too quickly. A 20-gallon long (30 inches wide, 12 inches tall, 12 inches deep) is a common starting size because it gives fish horizontal swimming room without taking up much floor space. A 40-gallon breeder (36 inches wide, 18 inches tall, 18 inches deep) or 55-gallon (48 inches wide, 13 inches tall, 12 inches deep) gives you more room to work and more stable water conditions.

Glass tanks come in standard dimensions from aquarium suppliers. You can also have glass cut to custom size at a glass shop, though this costs more and you will need to seal the seams yourself with aquarium silicone. Acrylic tanks are often custom-built by specialty makers. For routine maintenance purposes, a standard glass tank from a supplier is simpler and cheaper.

The stand must support the full weight. A 20-gallon long tank filled with water, gravel, and equipment weighs roughly 200 pounds. A 55-gallon weighs roughly 500 pounds. You can buy a stand rated for your tank size, build one from wood (using 2x4 lumber and exterior-grade wood screws), or use a sturdy table or cabinet you already own—as long as it does not flex when you press down on it.

Selecting and installing filtration

Filtration removes waste and keeps water chemistry stable. The three types are hang-on-back filters (clip to the rim, cheapest and easiest to maintain), canister filters (sit under the tank, more powerful, harder to clean), and sponge filters (air-driven, very gentle, best for small tanks or fry). For a beginner 20 to 55-gallon tank, a hang-on-back filter is usually the right choice.

Filter size is measured in gallons per hour (GPH). A rule of thumb is to choose a filter rated for 2 to 3 times your tank volume per hour. A 20-gallon tank should have a filter rated for 40 to 60 GPH. A 55-gallon should have one rated for 110 to 165 GPH. A stronger filter does not hurt; a weaker one leaves waste to build up.

Install the filter according to the manufacturer's instructions. Most hang-on-back filters clip to the back rim and draw water up a tube into the filter media, then return clean water to the tank. Fill the filter media (usually foam, charcoal, or ceramic) with water before turning it on, or it will suck air and make noise. The filter should run 24 hours a day.

Adding a heater and thermometer

Most tropical fish need water between 76 and 80 degrees Fahrenheit. A submersible heater sits inside the tank and maintains temperature automatically. Size the heater based on tank volume and how much you need to warm the water. A 50-watt heater works for a 10 to 20-gallon tank in a room that stays above 65 degrees. A 100-watt heater works for a 40 to 55-gallon tank or a colder room. If your room is very cold, go up a size.

Place the heater near the filter outlet so warm water circulates throughout the tank. Use a separate thermometer to check temperature daily for the first week, then weekly after that. Stick-on thermometers are cheap but less accurate; a floating or digital thermometer is more reliable.

If you plan to keep cold-water fish like goldfish or corydoras, you may not need a heater at all—room temperature is often enough. Research the fish species before you buy equipment.

Installing lighting and substrate

Lighting serves two purposes: it lets you see the fish, and it powers photosynthesis if you keep live plants. An LED light is energy-efficient and produces less heat than older fluorescent lights. Most aquarium lights clip to the rim or mount on a hood. A basic light rated for your tank size is fine; you do not need expensive programmable lights to start.

Run the light 8 to 10 hours a day. More than that can cause algae blooms. If you do not have a timer, set a phone reminder to turn the light on and off at the same time each day.

Substrate is the material on the bottom of the tank. Sand and gravel are the most common. Gravel is easier to clean and does not compact; sand looks more natural and is better for fish that dig or sift. Use 1 to 2 pounds of substrate per gallon. Rinse gravel or sand thoroughly in a bucket before adding it to the tank, or the water will be cloudy for days.

Cycling the tank before adding fish

Cycling means letting beneficial bacteria establish in the filter and substrate. These bacteria convert fish waste (ammonia) into less toxic compounds. Without them, ammonia builds up and kills fish. Cycling takes two to four weeks and happens whether you add fish or not—you just control whether fish are in the tank while it happens.

The safest method is fishless cycling: add ammonia (pure ammonia from a hardware store, or fish food that breaks down into ammonia) to bring the level to 2 parts per million, then test the water every few days with a liquid test kit. When ammonia drops to zero and nitrite (the intermediate compound) also drops to zero, the cycle is complete. Then do a 50% water change and add fish slowly—a few at a time over a week or two.

Some people cycle with fish, adding hardy species first and accepting that ammonia will spike. This is riskier because the fish experience stress and may die. If you go this route, do 25% water changes every other day and add only a few fish at first.

Testing water and making adjustments

A liquid test kit measures ammonia, nitrite, nitrate, and pH. These are the four numbers you need to know. Buy a kit that tests all four; strips are cheaper but less accurate. Test the water every day for the first two weeks, then weekly for the first month, then every two weeks once the tank is stable.

Ammonia and nitrite should stay at zero. Nitrate will climb over time and should stay below 40 parts per million; if it rises higher, do a 25% water change. pH depends on your fish species—most tropical fish are fine between 6.5 and 7.5, but research your specific fish.

If ammonia or nitrite stays high after a week, the filter may be too small, you may have overstocked the tank, or you may be overfeeding. Cut back on food first (fish only need what they can eat in 2 to 3 minutes), then consider a larger filter or fewer fish.

Stocking the tank with fish and plants

Once the cycle is complete and water parameters are stable, add fish slowly. A common rule is one inch of fish per gallon of water, but this varies by species—some fish are active and produce more waste, others are calm and produce less. Research each species before you buy.

Add fish in small groups over one to two weeks. This gives the bacteria time to adjust to the increased bioload. If you add 20 fish at once, ammonia will spike and some fish will die.

Live plants are optional but helpful. They consume nitrate, produce oxygen, and give fish places to hide. straightforward plants for beginners include java fern, anubias, and amazon sword. Plant them in the substrate or tie them to rocks and driftwood with fishing line. They do not need special fertilizer to start.

Frequently Asked Questions

Can I use tap water straight from the faucet?

Yes, but treat it first with a water conditioner to remove chlorine and chloramine, which kill beneficial bacteria and harm fish. A bottle of conditioner costs a few dollars and lasts months. Add the dose recommended on the bottle each time you do a water change.

How often should I clean the filter?

Rinse the filter media in old tank water (not tap water) every two to four weeks, depending on how dirty it looks. Do not replace the media unless it falls apart; you want to keep the bacteria that live in it. Replace only the charcoal layer if your kit has one, since charcoal wears out.

What if the water turns cloudy after I fill the tank?

Cloudy water usually means you did not rinse the substrate enough, or bacteria are blooming during the cycle. It will clear on its own in a few days. Do not do a water change or add chemicals; just wait and let the filter run.

Do I need a backup power supply if the power goes out?

A battery-powered air pump is cheap insurance. It keeps water oxygenated for a few hours if the filter stops. For a long outage, the tank will survive a day or two without power as long as you do not panic and do large water changes when power returns.

Can I move the tank once it is set up?

Yes, but it is stressful for the fish and the bacteria. If you must move it, drain most of the water into clean buckets, move the tank and stand, then refill with the same water. Keep the filter running the whole time if possible. Do not break down the tank and rebuild it unless you have to.