Start with the right tank size and shape for your space and fish
The tank itself is your foundation, and size matters more than most beginners realize. A larger tank is actually easier to maintain than a small one because water chemistry changes more slowly when there is more water to dilute waste. A 20-gallon tank is a practical starting point — big enough to be forgiving, small enough to fit in most homes and not cost a fortune to fill and heat.
Glass tanks are standard and affordable. Acrylic tanks are lighter and less likely to shatter, but they scratch more easily and cost more upfront. Decide whether you want a rectangular tank (easiest to work with), a tall tank (takes up less floor space but limits fish options), or a bow-front tank (looks nice but harder to clean and more expensive). Your choice depends on where the tank will sit and what fish you plan to keep.
Before you buy, measure your space and check that the surface underneath can hold the weight. A filled 20-gallon tank weighs about 170 pounds. A 55-gallon tank weighs roughly 485 pounds. Make sure your stand or furniture is rated for that load.
Key Takeaways
- Start with a 20-gallon tank or larger, as bigger tanks are more stable and forgiving for beginners.
- You need a filter rated for your tank size, a heater (unless you keep cold-water fish), an air pump or powerhead for water movement, and a light if you want to see the fish or grow plants.
- Gravel or sand substrate, rocks, and plants create hiding spaces and help beneficial bacteria colonize the tank.
- Cycle your tank for two to four weeks before adding fish so that bacteria can break down waste and keep the water safe.
- Test water parameters weekly for the first month, then monthly once the tank is stable.
Choose a filter strong enough for your tank volume and fish load
The filter is the engine of your aquarium. It removes solid waste, breaks down harmful chemicals, and provides surface area for beneficial bacteria to live on. A filter should process the entire tank volume at least three times per hour — so for a 20-gallon tank, you want a filter rated for 60 gallons per hour (GPH) or higher.
The three main types are hang-on-back filters (cheap, straightforward to maintain, good for beginners), canister filters (powerful, hidden, more expensive), and sponge filters (straightforward, quiet, best for small tanks or breeding setups). For a first aquarium, a hang-on-back filter is usually the right choice. It clips to the rim of the tank, takes up no floor space, and you can clean it in minutes.
When you buy a filter, it comes with filter media — usually foam, charcoal, and biological media. The foam catches solid waste, the charcoal removes odors and discoloration, and the biological media is where the bacteria live. You will replace the foam and charcoal every month or two, but never replace all the media at once or you will lose the bacteria.
Add a heater and light suited to your fish and tank size
Most tropical fish need water between 75 and 80 degrees Fahrenheit. A submersible heater with a thermostat will maintain that temperature automatically. For a 20-gallon tank, a 100-watt heater is standard. For a 55-gallon tank, use 200 watts. If your room is already warm or you plan to keep cold-water fish like goldfish, you may not need a heater at all.
Lighting serves two purposes: it lets you see the fish, and it drives photosynthesis if you keep live plants. A basic LED light strip that clips to the tank rim costs $20 to $50 and works well for most setups. If you plan to grow demanding plants, you will need a stronger light and a timer to run it 8 to 10 hours per day. Without a timer, algae will grow faster than plants can use it.
An air pump and airstone are optional but useful. They create bubbles that increase water movement and oxygen at the surface. This is especially helpful in tanks without plants or in warm water, where oxygen dissolves more slowly. A small air pump costs $15 to $30.
Layer substrate, rocks, and plants to create a stable environment
Substrate is the material on the bottom of the tank. Gravel and sand both work, but sand looks more natural and is easier to clean. Gravel is cheaper and easier to plant in. For a 20-gallon tank, buy 30 to 40 pounds of substrate. Rinse it thoroughly before adding it to the tank — even "pre-rinsed" gravel has dust that will cloud the water.
Rocks and driftwood serve two jobs: they look good and they provide hiding spaces where fish feel safe and where beneficial bacteria can colonize. Lava rock, slate, and smooth river rocks are all safe. Avoid rocks with sharp edges or unknown origin. Driftwood is sold at aquarium stores and is safe to use. Boil it first to remove tannins that will stain the water brown.
Live plants are not required, but they help. They consume nitrate (a waste product that builds up over time), 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 with fishing line. Plastic plants work too, but they do not help with water chemistry and can tear fish fins.
Cycle the tank for two to four weeks before adding fish
Cycling is the process of establishing the bacteria colony that keeps the tank safe. Without it, fish waste (ammonia) builds up to toxic levels and kills the fish. The cycle happens in stages: ammonia-eating bacteria colonize the filter and substrate, then nitrite-eating bacteria follow, and finally the system stabilizes with ammonia and nitrite at zero and nitrate present but low.
The easiest way to cycle is the fishless cycle. Add ammonia (from a bottle or by decomposing fish food) to bring the level to 2 parts per million (ppm). Test the water every few days with a liquid test kit. When ammonia drops to zero and nitrite appears, the first bacteria are working. When nitrite drops to zero and nitrate appears, the cycle is complete. This usually takes two to four weeks.
An alternative is the fish-in cycle, where you add hardy fish and do frequent water changes to keep ammonia and nitrite low while bacteria colonize. This is harder on the fish and requires daily testing, so fishless cycling is better if you have the patience.
Test water parameters weekly until the tank is stable
A liquid test kit measures ammonia, nitrite, nitrate, and pH. These are the four numbers that tell you whether the tank is safe. After cycling, ammonia and nitrite should always be zero. Nitrate will climb over time and should be kept below 40 ppm by doing partial water changes (remove 25 to 50 percent of the water and replace it with fresh water).
pH is how acidic or basic the water is, measured on a scale from 0 to 14. Most fish prefer pH between 6.5 and 7.5. pH changes slowly in an established tank, so you do not need to adjust it unless it drifts far from where it started. Test weekly for the first month, then monthly once the tank is stable and you understand how your tank behaves.
Do not use test strips — they are less accurate than liquid kits and cost more over time. A liquid kit like the API Master Test Kit costs $25 to $35 and lasts for hundreds of tests.
Assemble the tank in the right order to avoid mistakes
Place the empty tank on its stand and check that it is level using a spirit level. An unlevel tank will stress the glass and may leak. Add the substrate, then fill the tank halfway with water. Add rocks, driftwood, and plants. Fill the tank the rest of the way. Install the heater, filter, and light. Turn everything on and let it run for a few hours to make sure there are no leaks.
Once water is circulating and the heater is warming the tank, begin the cycling process. Do not add fish yet. If you are doing a fishless cycle, add ammonia now. If you are doing a fish-in cycle, wait 24 hours for the water to reach temperature, then add a few hardy fish like danios or tetras.
Keep a log of your test results and water changes. This helps you spot problems early and understand how your tank responds to different conditions. After a few months, you will know your tank well enough to troubleshoot on your own.
Frequently Asked Questions
How much does it cost to build a basic aquarium?
A 20-gallon setup with tank, stand, filter, heater, light, substrate, and basic decorations costs between $150 and $300. A test kit adds $25 to $35. The cost depends on whether you buy budget brands or premium equipment. Budget brands work fine for beginners.
Can I use tap water straight from the faucet?
Tap water contains chlorine and chloramine, which kill beneficial bacteria and harm fish. Use a dechlorinator product (liquid or powder) to remove these chemicals before adding water to the tank. Most dechlorinators work when ready, so you can add water and dechlorinator at the same time during water changes.
What fish should I start with?
Choose hardy, peaceful fish that tolerate a range of water conditions. Neon tetras, guppies, corydoras catfish, and danios are all good choices for a first tank. Avoid large fish, aggressive fish, and fish that need very specific water conditions. Research each species before you buy to make sure it fits your tank size and temperament.
How often should I do water changes?
Once the tank is cycled and stable, do a 25 to 50 percent water change every week or two. This removes nitrate and waste that the filter cannot break down completely. In a new tank during the first month, you may need to change water more often if ammonia or nitrite stays above zero.
What if the tank gets cloudy or smells bad?
Cloudiness usually means bacteria are blooming because ammonia or nitrite is high, or because you overfed the fish. Stop feeding for a day, do a 50 percent water change, and test the water. A bad smell means waste is building up — increase water changes and check that the filter is clean and running properly.