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setup · freshwater
Beginner freshwater aquarium setup
A heated, filtered 20-gallon tank is a kinder first aquarium than a tiny kit. Cycle before you add fish, test your water, and stock slowly.
Published 2026-04-02 · Updated 2026-08-15
Start with the box, not the fish
Pick the fish after you know your tank size, your tap water, and whether you want tropical or coldwater. Buying a betta, a goldfish, and a saltwater clownfish on the same receipt is how mixed, doomed communities start.
A 20-gallon aquarium on a dedicated stand, with a tight lid, is a practical first build. Place it away from heaters, direct sun, and high-traffic slamming doors. Water weighs about 8.3 pounds per gallon plus the glass, stand, and rock — treat the floor and stand as load-bearing, not decorative.
Core equipment
Heater with a thermometer you can actually read (do not trust the heater dial alone). Filter rated for the tank or a bit above — sponge filters are gentle and cheap; hang-on-back filters are common in kits. Dechlorinator. A liquid test kit for ammonia, nitrite, nitrate, and pH. Gravel vacuum and a bucket that will never see soap.
Substrate can be sand for cories or a simple gravel. Rinse it. Hardscape should be aquarium-safe; some woods and rocks leach tannins or raise hardness. Live plants are optional but they help with water quality if light is modest and you do not overdose fertilizer.
Fill, heat, cycle
Fill with tap water treated to remove chlorine or chloramine. Set the heater into the mid-70s °F for tropical fish. Run the filter. Then cycle — fishless if you can wait. Our cycling guide walks through tests and timing.
Do not add fish, snails 'to clean,' or a handful of plants from a bag of water that never got tested, all on day one. Snails and plants can hitchhike pests; they also add bioload.
First stocking ideas
A 20-gallon tropical tank might hold a school of neon tetras plus a group of peppered cories, or a small group of guppies (males only if you do not want fry). A single betta can live in 5–10 gallons; in 20 gallons you have room for careful community mates if the betta is calm.
Skip goldfish, oscars, and common plecos in this footprint. Read the species pages before you shop. Stock in groups when the fish is a schooler, and add slowly so the filter can keep up.
Weekly rhythm
Test until you are bored of testing, then keep testing after water changes and new fish. Change about 25–40% weekly, vacuum debris, rinse filter media in old tank water only when flow is actually clogged. Feed small portions that disappear in a couple of minutes.
If something looks wrong — gasping, clamped fins, cloudy water — test ammonia and nitrite before you buy a random bottle of medication.
Frequently asked questions
What size tank should a beginner buy?+
A 20-gallon tank is a sweet spot: large enough to stay more stable than a 5-gallon, small enough to lift, fill, and place on a proper stand. Five gallons can work for a single betta if you accept more frequent maintenance.
Do I need a heater?+
For tropical freshwater fish, yes in most homes. Goldfish are the common exception — they want cooler water and a much larger tank.
When can I add fish?+
After the tank has cycled. See our cycling guide. Adding livestock on setup day is the most common way to kill a first tank.