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Setting up a freshwater aquarium

Most first-tank problems are planning failures, not equipment failures. This checklist covers the steps and the common mistakes — in the order that actually matters before the water goes in.

1. Choose the right tank size for your fish

Minimum tank sizes are based on adult fish, not juveniles sold in shops. A 20L 'starter kit' is suitable for a shrimp colony or a single betta — not a community of tetras. Check the minimum tank for every species you plan to keep before buying the tank.

2. Plan stocking before cycling

Decide your full stocking list before you fill the tank. Fish that look compatible as juveniles may not be at adult size. Run pair checks and use the tank builder to verify the combination before you commit to a tank size or hardscape layout.

3. Cycle the tank before adding fish

Biological cycling establishes ammonia-converting bacteria in your filter media. Fishless cycling takes 3–6 weeks with an ammonia source. Do not add fish to an uncycled tank — ammonia spike is the single most common cause of early fish deaths.

4. Choose substrate to match your fish and plants

Fine sand or smooth gravel suits corydoras and bottom-dwelling catfish; coarse gravel can damage their barbels. Planted tanks benefit from nutrient-rich substrates (e.g. aquasoil). Bare-bottom setups make cleaning easier for messy fish like goldfish or large cichlids.

5. Hardscape before water

Arrange rocks, driftwood, and decorations before filling. Once fish are in, rearranging disturbs territory and stresses fish. Aquascape with adult fish size in mind — tight caves and narrow passages become traps when cichlids are full-grown.

6. Add plants at setup or before fish

Plants establish faster without fish. Low-light, no-CO2 species (Java Moss, Anubias, Java Fern) are the safest choices for a new tank and help compete with algae during the break-in period.

7. Stock in stages

Add fish gradually over weeks, not all at once. The filter bioload capacity builds over time. Overstocking on day one before the biological colony has scaled up is a common cause of ammonia spikes in a tank that has been cycled.

8. Establish a maintenance routine

Weekly 25–30% water changes are a baseline for most community tanks. Test water parameters (ammonia, nitrite, nitrate) in the first months. Once the tank matures and nitrate is the only thing you are managing, you can adjust the frequency.

Most common first-tank mistakes

  • Buying fish on the day of setup — the tank needs to cycle first.
  • Choosing a 'starter kit' that is too small for the fish on the box.
  • Under-sizing the filter for the actual stocking load at adult size.
  • Mixing fish from very different water parameters (soft + hard; cold + tropical) because both were available at the shop.
  • Adding all fish at once in the first week.
  • Not researching adult size — common plecos reach 45–60cm and are sold as tank cleaners for small tanks.
  • Buying fish because they looked good together in the shop display — displays are not long-term communities.

Plan before you buy