Clean and professional customer waiting area with beautiful aquarium

Choosing the Right Aquarium Size – Fish Tank Size Guide

Find the perfect home for your fish — from first tank to full community setups.

At Birchwood Aquatic Centre, we know that the size of your aquarium is one of the most important decisions you’ll make. The tank you choose affects everything from water stability and maintenance, to fish health and future upgrades. Whether you’re setting up your first nano aquarium or a large show tank, we can help you make the right choice.

Why Aquarium Size Matters

A larger tank might seem more intimidating at first, but in most cases, bigger is easier. Small tanks fluctuate in temperature and water quality much faster, which can stress or even harm your fish.

Larger tanks offer:

  • More stable water conditions (less risk of ammonia or pH swings)
  • Happier, healthier fish with room to swim and grow
  • Easier maintenance as waste is diluted more effectively
  • More aquascaping options for plants, rocks, and ornaments

Even beginners benefit from starting with a tank of at least 60 litres. Smaller tanks (such as 20L) are best suited to shrimp or a single Betta fish.

Matching Tank Size to Your Fish

The type of fish you keep will determine the ideal tank size. Always research the adult size of each species — not just how big they are when you buy them!

Fish Type Minimum Tank Size Example Species
Betta or small nano species 20–30 litres Betta, Ember Tetra
Small community tank 60–100 litres Guppies, Platies, Corydoras
Medium tropical setup 100–180 litres Angelfish, Gourami, Rainbowfish
Large community tank 180–300 litres Discus, larger barbs or tetras
Marine or reef setup 100L+ Clownfish, Gobies, Soft Corals
Coldwater or fancy goldfish 100L+ Orandas, Fantails, Ryukin

Tip: Goldfish produce a lot of waste — always go larger than you think!

Planning for Growth and Maintenance

When choosing a tank, think about the long term:

  • Will your fish grow significantly?
  • Do you plan to add more species later?
  • Do you have space for equipment (filter, heater, lighting)?
  • Is your cabinet or stand strong enough to support the tank’s weight?

Remember: 1 litre of water = 1 kilogram of weight. A 200-litre aquarium can weigh over 250kg once filled!

Beginner Recommendation

If you’re new to the hobby, we suggest:

  • Tropical Starter Setup (around 60–100L) – easy to heat and maintain, with space for a small community
  • Include: filter, heater, lighting, gravel/sand, plants, and décor

 

Frequently Asked Questions


Not necessarily. Small tanks look simpler but are harder to keep stable. Temperature and ammonia levels can spike quickly, making maintenance more challenging.


We recommend 60–100 litres. It’s large enough to stay stable and give your fish room to thrive, yet still compact for most homes.


A common rule is 1 inch of fish per 1 gallon (4.5L), but this is only a rough guide. Species activity, filtration, and aquascaping all affect stocking levels.


Yes! Many fishkeepers start small and move up as their experience and fish collection grow. Just make sure to transfer existing filter media and water to help seed your new tank.


Always use a purpose-built aquarium cabinet or stand. Water is heavy — even a 60L tank weighs around 70kg once set up.


Absolutely. Fancy goldfish produce a lot of waste and need plenty of swimming room. Start with at least 100 litres for one or two fish.


Avoid direct sunlight as it causes temperature swings and algae growth. Choose a level, stable surface away from radiators and windows.

Visit Birchwood Aquatic Centre

Come and see our full range of aquariums, stands, filters, and starter kits in-store. Our friendly team can help you:

  • Choose the ideal size for your fish and space
  • Match compatible species
  • Set up and cycle your tank correctly

Birchwood Aquatic Centre, London Road, Swanley, Kent 01322 664397