Maya LindqvistSep 18, 20268 min read
A planted freshwater setup. The tank was cycled and planted long before the first fish went in.
Setting up a first fish tank is a two-week project, not a one-afternoon errand. Almost every avoidable early failure traces back to the same mistake: adding fish before the tank is ready. This guide walks the whole process in the order that works, so your first fish have every chance of thriving.
Choose the biggest tank that fits
Bigger water volume is simply more forgiving. A 20-gallon (75 liter) tank stays warmer, filters cleaner, and resists swings in water chemistry far better than a small bowl or a 5-gallon desk tank. As a rule for a first community tank, buy the largest size your stand and floor can comfortably take, and keep at least 10 gallons if you want to keep more than one or two small fish. Bowls and jars are scenery for a single small creature at best; they are not a starting point for a beginner community.
Get the four essentials before the fish
- Filterrated for your tank size or slightly larger. Hang-on-back and internal filters are fine; the goal is gentle water movement and biological filtration.
- Heater. Plan roughly 3 to 5 watts per gallon, and buy a model with a thermostat. Most community fish want water around 24-27°C (75-80°F).
- Lighton a timer or a habit: about 8 hours a day, and less while you are still setting up.
- Liquid test kitfor ammonia, nitrite, nitrate, and pH. Test strips are fine for occasional checks, but a liquid kit is what you want during cycling.
Substrate and hardscape come first
Rinse your substrate in a bucket until the water runs clear, then spread it 2 to 3 inches deep, deeper where you plan to put rooted plants. Plain aquarium sand or inert gravel is fine and cheap. Add rocks and wood you can identify as aquarium-safe (slate, lava rock, dragon stone, and properly prepared driftwood), arrange them so there are no dead spots, and fill the tank slowly so the sand stays put. Nothing in this tank is alive yet, which is exactly the point.
Fill, filter, heat, and dechlorinate
Connect the filter and heater, fill the tank, and treat the tap water with a dechlorinator to remove chlorine and chloramine. Let everything run for 24 hours and confirm the heater holds your target temperature. Your tank now looks finished. Nothing should go in it for at least two weeks.
Cycle the tank before adding fish
Fish waste becomes ammonia, and ammonia is toxic. A cycled tank is one where beneficial bacteria have established that convert ammonia to nitrite, and nitrite to the far less harmful nitrate. This takes two to six weeks.
To cycle without fish, add a small ammonia source (liquid ammonia dosed to about 2 ppm, or a tiny pinch of fish food every couple of days) and test daily. When ammonia and nitrite both read zero and nitrate has appeared, the cycle is done. Do a large water change, then add your first fish a day later. It is boring, it takes patience, and it is the single most important step in this guide.
Add plants, then a few fish, slowly
Plant the easy species from ourbeginner plants guidebefore adding fish. Plants consume nitrate, give fish places to hide, and make a new tank look settled instead of sterile. Then add fish in small groups, one group every one to two weeks, so your filter bacteria can keep up with the growing load. Quarantine any new fish in a separate tank for two weeks if you can; it is the cheapest insurance against disease.
Your first 30 days, week by week
- Days 1-3:place the tank and stand, install and test the equipment.
- Days 4-10:rinse substrate, build the hardscape, fill and dechlorinate.
- Days 11-20:cycle fishless. Test ammonia and nitrite daily.
- Days 21-28:plant easy species, wait two days, add one small hardy group of fish and feed very lightly.
- Day 30:start the weekly rhythm: one 20-25% water change, one filter check, one feeding skip day.
Freshwater or saltwater: which should you start with?
This guide is about freshwater, and that is a deliberate choice for a first tank. The table below is the honest summary we wish someone had given us.
Frequently asked questions
Two to six weeks with a fishless cycle. Ammonia and nitrite must both read zero before fish. Test daily, stay patient, and let the tank tell you when it is ready.
Most cloudiness is a bacterial bloom, normal in the first weeks. It clears on its own. Keep feeding light and do not wash the filter media while it settles.
About 20 to 25 percent once a week is a steady rhythm most freshwater tanks do well on. Small weekly changes beat big monthly ones.
Keep reading
Your tank is cycled and your first fish are home. Next, choose species that will actually get along in ourguide to beginner-friendly freshwater fish, and set a feeding routine withour feeding guideso the tank stays clean.
Maya Lindqvist
Maya keeps planted community tanks and runs the setup guides at Worlds Fish.
Related articles
- Aquarium Plants 101: Easy Greenery for a Healthier Tank8 min read
- 10 Freshwater Fish That Are Perfect for Beginners7 min read
- How Often Should You Feed Your Fish?5 min read
New posts by email
One short email a week with the newest guides.