Setting up an aquarium for beginners: the complete checklist for a healthy start

July 18 2026, by Michael van Wassem, 6 min reading time

Setting up an aquarium? Here's how to set it up, cycle it safely, and choose the right fish - including a checklist and common mistakes.

An aquarium sounds like a simple purchase: a tank, water, fish. Yet the most common beginner mistake - adding fish too soon - is what causes illness or losses within the first few weeks. With the right preparation, you can avoid this entirely.

Quick answer: Set up the aquarium fully first, with substrate, decoration, a filter and a heater, fill it with water, and let it "cycle" for at least 3 to 6 weeks before adding your first fish. During this period, an invisible colony of beneficial bacteria builds up that breaks down harmful waste products. This cycling process - the nitrogen cycle - is the step beginners skip most often, and the leading cause of problems in the first few weeks.

Which aquarium should you choose?

The size of the aquarium largely determines how stable the water stays. It sounds counterintuitive, but a larger aquarium is actually easier for beginners: in a small volume of water, temperature and water parameters swing much faster, which stresses fish.

• Nano aquarium (up to about 30 litres): suitable for shrimp or a single small fish species, but less forgiving of beginner mistakes.
• Medium aquarium (60-120 litres): the most comfortable starting point for most beginners, with room for a small group of shoaling fish.
• Large aquarium (120+ litres): more stable water, but also a bigger investment in space and equipment.

Choose a tank that suits the space you have and the type of fish you have in mind.

The basic equipment: what do you need?

An aquarium is more than a tank of water. For a healthy ecosystem, you need at least:

• A filter - keeps the water clear and houses the beneficial bacteria that keep your aquarium in balance.
• A heater - most community fish need a stable water temperature between 24 and 26 °C.
• Lighting - important for your fish's day-night rhythm and, if you keep plants, for their growth.
• Substrate - gravel or aqua soil, matched to any plants and to bottom-dwelling fish species.
• Decoration and hiding spots - rocks, roots or plants give fish structure and reduce stress.

Not every type of gravel is suitable: a substrate made specifically for aquariums is rounded and won't negatively affect the water parameters. Add decoration that provides hiding spots, especially if you later choose fish that need them.

Cycling the aquarium: the nitrogen cycle

This is the step that prevents most beginner problems. Fish excrete ammonia, which is toxic at high concentrations. In a cycled aquarium, bacteria in the filter and substrate convert ammonia into nitrite, and then into the far less harmful nitrate. Without these bacteria, ammonia and nitrite levels in a new aquarium rise within days to a level that makes fish ill - known as "new tank syndrome".

In practice, this means:

• Fill the aquarium and run the filter and heater for at least 3 to 6 weeks before any fish go in.
• A water conditioner and a bacterial starter help build up the right bacterial culture faster.
• Test the water parameters (ammonia, nitrite, nitrate, pH) with a test kit before adding fish: only once ammonia and nitrite read 0 is the aquarium ready.
• Add fish afterwards in small groups, a few weeks apart, so the bacterial culture can grow along with the bioload.

A good water conditioner and bacterial starter are essential for this stage: conditioners make tap water safe by neutralising chlorine, and bacterial starters noticeably speed up cycling.

Which fish should you choose as a beginner?

Not every fish is suited to starting out with. Choose species known to be hardy and that do well in groups, such as various tetras, guppies, platies or neons. As a beginner, avoid large predatory fish, fish with very specific water requirements, or species that eventually grow large - if in doubt, always ask about a species' adult size and behaviour before taking it home.

Also pay attention to group size: many community fish are shoaling fish that only feel comfortable in a group of at least five to six. Keeping a single fish on its own causes ongoing stress.

Feeding and daily care

Most community fish do well on flake or pellet food, matched to their species and size. Alternate this with frozen food or tablets for bottom-dwelling fish, so your fish get a varied diet without overfeeding. Don't feed more than your fish can eat in two to three minutes: leftover food pollutes the water and disrupts the balance you've just built up.

Choose food suited to the specific species you keep, from tropical fish to goldfish.

Alongside feeding, weekly care includes: a partial water change of about 10 to 20%, cleaning the glass, and checking the filter and heater.

Checklist: setting up an aquarium in 6 steps

1. Choose an aquarium that suits your space and the fish species you have in mind.
2. Set up the tank with substrate, decoration, a filter and a heater.
3. Fill the aquarium with water and a water conditioner.
4. Let the aquarium cycle for 3 to 6 weeks and test the water parameters regularly.
5. Only add fish once ammonia and nitrite read 0, in small groups at a time.
6. Feed in moderation and change part of the water weekly.

Common mistakes with a new aquarium

• Buying fish on the day you get the aquarium - the aquarium hasn't had time to cycle.
• Adding a whole group of fish at once - this overloads the still-young bacterial culture.
• Overfeeding - leftover food pollutes the water and disrupts the balance.
• Thoroughly cleaning or replacing the filter - this washes away the very beneficial bacteria you've built up. Only rinse filter media gently in water taken from the aquarium.
• Not testing water parameters - without testing, a disrupted balance stays invisible until the fish are already ill.

Frequently asked questions

How long does an aquarium need to cycle before fish can go in?
Allow at least 3 to 6 weeks, depending on whether you use a bacterial starter. Always test the water parameters before adding fish, rather than relying on a fixed period.

Can I add all my fish at once right after cycling?
No. Add fish in small groups a few weeks apart, so the bacterial culture can grow along with the amount of waste.

How often should I change the water?
A partial water change of 10 to 20% a week keeps water quality stable without disrupting the bacterial culture.

Do I always need a heater?
For most tropical community fish, yes. Cold-water fish such as some goldfish varieties can do without one, but always check for the specific species.

Summary and conclusion

A healthy aquarium doesn't start with the fish, but with patience: set up first, then let it cycle, and only then add residents. Following this order and keeping an eye on the water parameters avoids most of the problems beginner fishkeepers run into. That way, an aquarium grows into a stable, calming environment for your fish - and a lovely piece of nature at home.

Disclaimer: this article is intended as general information. If in doubt about specific fish species or water parameters, consult a specialist retailer or vet.

Tags

Aquarium Informatie Vissen

• Share on:
• WhatsApp
• Deel
• X
• Pin it
• Messenger
• Email