Choosing the right fish for your aquarium is one of the most important decisions you’ll make as a fish keeper.
Get it right, and you’ll have a peaceful, thriving tank.
Get it wrong, and you can end up with stressed fish, aggression, or even losses.
At Top Fin Aquatics, we help hobbyists across New Zealand avoid those mistakes by matching fish to the right setups from the start.
In this guide, we’ll walk you through exactly what to consider before adding fish to your tank.
1. Tank Size Matters More Than You Think
One of the biggest mistakes beginners make is choosing fish based on appearance—not tank size.
Every fish has:
- A minimum tank size
- Space requirements for swimming
- A bioload (waste output)
General Rule:
- Small tanks (20–60L): stick to nano fish
- Medium tanks (60–150L): community fish
- Large tanks (150L+): larger species or mixed setups
Overstocking leads to poor water quality, stress, and algae problems.
2. Temperament and Compatibility
Not all fish get along—even if they look peaceful.
Before choosing fish, ask:
- Are they aggressive, semi-aggressive, or peaceful?
- Will they nip fins?
- Do they need to be kept in groups?
Examples:
- Tetras = peaceful, schooling fish
- Cichlids = often territorial
- Livebearers = generally community-friendly
Mixing incompatible fish is one of the fastest ways to create problems in your tank.
3. Water Parameters and Conditions
Different fish require different water conditions.
Key Things to Check:
- Temperature
- pH level
- Hardness
Most tropical fish in NZ setups do well in:
- 24–26°C
- Neutral pH
But always double-check before mixing species.
4. Tank Setup and Environment
Your aquascape plays a big role in what fish you can keep.
Consider:
- Do you have plants?
- Is there enough hiding space?
- Open swimming areas?
Examples:
- Bettas prefer calm water and cover
- Schooling fish need open swimming space
- Bottom dwellers need substrate and hiding spots
Matching fish to your environment reduces stress and improves behaviour.
5. Schooling vs Solo Fish
Some fish must be kept in groups to feel safe.
Schooling Fish:
- Tetras
- Rasboras
- Corydoras
These should be kept in groups of 6 or more.
Solo or Pair Fish:
- Bettas
- Some cichlids
Keeping schooling fish alone often leads to stress and poor health.
6. Feeding and Maintenance Requirements
Different fish have different care levels.
Ask yourself:
- Do they need special food?
- Are they messy eaters?
- How often do they need feeding?
Choosing fish that match your routine makes long-term success much easier.
7. Experience Level
Some fish are beginner-friendly, others are not.
Great Beginner Fish:
- Guppies
- Platies
- Tetras
- Corydoras
More Advanced Fish:
- Discus
- Sensitive shrimp setups
- Certain cichlids
Starting simple helps you build confidence and avoid early setbacks.
8. Is Your Tank Fully Cycled?
Before adding any fish, your tank must be fully cycled.
If not, ammonia and nitrite will spike and harm your fish.
If you’re unsure, check out our cycling guide or use proven products to speed things up.
9. Think Long-Term (Growth & Lifespan)
Some fish sold small will grow significantly.
Always consider:
- Adult size
- Lifespan
- Future tank upgrades
Planning ahead prevents overcrowding and rehoming issues.
Build a Balanced Aquarium
A well-balanced tank usually includes:
- Top swimmers (e.g. tetras)
- Mid-level fish (e.g. livebearers)
- Bottom dwellers (e.g. corydoras)
This creates a natural, active aquarium without overcrowding one area.
Common Mistakes to Avoid
- Buying fish based on looks alone
- Adding too many fish at once
- Mixing incompatible species
- Ignoring tank size requirements
- Skipping the cycling process
Final Thoughts
Choosing the right fish isn’t about what looks best—it’s about what works best together in your setup.
When you match:
- Tank size
- Water conditions
- Fish temperament
- Your experience level
You’ll create a tank that is easy to maintain and enjoyable long-term.
Need Help Choosing the Right Fish?
Browse our carefully selected livestock here:
https://www.topfinaquatics.co.nz/collections/fish