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
Is a small tank easier to maintain?
Not necessarily. Small tanks look simpler but are harder to keep stable. Temperature and ammonia levels can spike quickly, making maintenance more challenging.
What is the best size for beginners?
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.
How many fish can I keep in my tank?
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.
Can I upgrade later to a bigger tank?
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.
What about weight and furniture support?
Always use a purpose-built aquarium cabinet or stand. Water is heavy — even a 60L tank weighs around 70kg once set up.
Do goldfish really need such big tanks?
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.
Can I put my aquarium near a window?
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