How to Set Up a Fish Tank for Beginners

The golden rule for beginners: cycle your tank before adding any fish. Setting up the tank and adding fish the same day is the most common beginner mistake and the biggest cause of fish loss.

Last updated: 9 June 2026 · PetsRus Team

What you need

• A tank as large as you can manage (bigger is more stable), a filter and a heater (for tropical fish).
• Substrate, a water-conditioner (dechlorinator) and a test kit.

Step by step

• Rinse and set up the tank, substrate and equipment.
• Fill with dechlorinated water and run the filter.
• Cycle the tank for several weeks until the filter grows the bacteria that process fish waste (the nitrogen cycle).
• Add fish slowly, a few at a time, and keep up regular partial water changes.

Frequently asked questions

What is cycling?

Growing beneficial bacteria that convert toxic ammonia into safer compounds. Test kits tell you when it's safe for fish.

How many fish can I add?

Start small and understock — overstocking spikes waste and stresses fish.