Betta Fish Tank Setup (UK): Step-by-Step Guide for 20–40L Tanks (Beginner-Friendly)

A betta fish tank setup in the UK is not the same as following the typical 5-gallon advice you see online. 

Most guides are built around US nano kits, vague temperature tips, and ignore what really matters in UK homes: colder rooms, fluctuating night temperatures, hard tap water, and tiny “betta kits” sold everywhere that simply don’t work long-term.

This guide fixes that.

You’ll learn exactly how to set up a betta tank in the UK, what to buy, how to assemble it, how to cycle it properly, and how to avoid the mistakes that stress (or kill) most bettas in their first month.

This is written for real beginners, using 20–40L tanks, practical equipment available in the UK, and a setup approach that prioritises stability, low flow, warmth, and plant cover.

Quick Answer: What is the ideal betta tank setup for beginners in the UK?

A proper UK betta setup needs:

• 20–40L tank (≈ 5–10 gallons)
• Heater set to 25–26°C (77–79°F) + thermometer
• Low-flow filter (sponge or adjustable internal/HOB)
• Lid (very important in UK homes)
• Live plants and hides near the surface
• Water conditioner (dechlorinator)
• Test kit (ammonia, nitrite, nitrate)
• Fishless cycle before adding the betta

If you get these right, you’re already ahead of most betta setups you’ll see online.

Quick Navigation (TOC)

• Shopping list: what you actually need
• 20L vs 30L vs 40L — best size for UK homes
• Heater & temperature (UK reality)
• Low-flow filtration explained
• Substrate, plants & betta-safe decor
• Step-by-step setup walkthrough
• Fishless cycling made simple
• Adding your betta + first week routine
• 3 layout ideas for 20–40L tanks
• Common mistakes to avoid
• FAQ
• Conclusion

Shopping List UK: What You Actually Need for a Betta Tank

Before setting up the tank, make sure you have all the equipment ready. This prevents rushing the process and avoids the most common beginner mistakes.

Essentials (NON-NEGOTIABLE)

How does this change depending on tank size

Bigger tanks are easier, not harder, for beginners.

Betta Fish Tank Setup Kit: Is It Worth It?

Most “betta kits” sold in shops are 2–3 gallons (10L) with:

• No heater
• Strong, non-adjustable filter
• No proper lid
• Not enough volume for stable water

Avoid them.

A kit is only worth buying if it allows:

• Heater installation
• Flow control (or space for sponge filter)
• Proper lid
• Minimum 20L capacity

If a kit can’t do these four things, it’s not suitable for a betta long-term.

20L vs 30L vs 40L: Best Betta Tank Size for UK Homes

You’ll often read that 5 gallons (≈19L) is the minimum for a betta.

That’s true.

But in real UK homes, with colder nights, temperature swings, and beginners still learning maintenance, 20–40 litres is where bettas actually thrive, and owners find the tank much easier to manage.

Why this range works so well

What changes between 10L, 20L and 40L (this is what most guides don’t explain)

This is why many beginners struggle with 10L kits and think bettas are “hard fish”, when the real issue is not enough water volume.

Why “5 gallons minimum (≈19L)” is correct, but incomplete

5 gallons (≈19L) keep a betta alive.
20–40L keeps the tank stable and the betta comfortable.

And stability is everything in UK homes, where:

• Room temperatures fluctuate
• The heating goes off at night
• Tap water parameters vary by region

More water = more stability = less stress for both fish and owner.

The sweet spot for most beginners

If you’re unsure:

• Choose 30L for the perfect balance
• Choose 40L if you have the space and want the easiest experience
• Choose 20L only if space is tight, but be ready to monitor more closely

Heater & Temperature (UK Reality): Keep It Stable Year-Round

Most betta guides simply say “keep the water warm”.

In UK homes, this is where most setups quietly fail.

Room temperatures often drop below 20°C at night, heating switches off, and small tanks lose heat fast. A weak or undersized heater can’t keep up, and temperature swings stress bettas more than slightly imperfect water parameters.

For a betta, stable warmth is more important than perfection.

Best temperature for bettas

Keep the tank at 25–26°C (77–79°F) consistently.

Not “around 24”.
Not “room temperature”.
Consistent warmth.

Always use a thermometer; don’t trust the heater dial.

Heater wattage guide for 20–40L tanks

Slightly oversizing the heater is safer than undersizing it.

Where to place the tank 

Placement affects temperature more than most beginners realise.

Avoid placing the tank:

• Next to windows (cold drafts, night chill)
• Near radiators (rapid heat swings)
• In drafty hallways
• On thin shelves exposed to cold air

Always use a lid. In UK homes, cold air above the water surface can cool the tank faster than you think.

Signs your heater is struggling

• Temperature drops overnight
• Betta becomes lethargic in the morning
• Condensation on the lid + fluctuating thermometer
• The heater is always running, but the temperature is still unstable

These are classic signs of an underpowered heater in a UK setup.

Filtration Without Strong Current: Choosing the Right Low-Flow Filter

Bettas are not built for strong currents.

In nature, they live in slow, shallow waters. In many beginner tanks, the filter creates a constant flow that feels like a river, forcing the betta to fight the current all day, which leads to stress, torn fins, and lethargy.

Good filtration is essential. Strong flow is not.

The goal is clean water with gentle circulation.

Best filter types for a betta tank

Avoid filters that:

• Have fixed, strong output
• Create a visible current across the tank
• Push the betta away from resting areas

How to reduce filter flow (easy beginner fixes)

Even a strong filter can be made betta-safe:

• Add a pre-filter sponge to slow intake and output
• Use a spray bar to disperse the flow
• Install a flow baffle (sponge or plastic guard)
• Point the outlet toward glass or decor, not open water

You should see the gentle movement of plants, not waves.

How to tell if the flow is too strong 

Signs the filter current is stressing your betta:

• The betta avoids one side of the tank
• Struggles to swim across the tank
• Hides constantly behind the decor
• Rests at the bottom more than near the surface
• Fins look pushed backwards while swimming

If you see these, reduce the flow.

Do bettas need an air pump?

Not for oxygen.

Bettas breathe from the surface using their labyrinth organ.

An air pump is only needed if:

• You use a sponge filter
• You want extra surface agitation in warm tanks
• The tank is heavily stocked (not typical for a single betta)

They still require good water quality and gentle circulation; breathing air does not replace filtration.

Substrate, Plants & Decor: Building a Betta-Safe Layout

Step-by-Step Betta Tank Setup (Beginner Walkthrough)

Follow these steps in order. Don’t rush. A calm, stable setup now prevents 90% of beginner problems later.

Step 1 - Pick the right location

Place the tank:

• Away from windows (cold at night, algae from sunlight)
• Away from radiators (temperature swings)
• Out of drafts and doorways
• On a level, sturdy surface

A stable location = stable temperature.

Step 2 - Rinse substrate and add hardscape

• Rinse gravel/sand with tap water until clear
• Place wood, rocks, and decor before adding water
• Check all decor for sharp edges

This is easier now than after the tank is full.

Step 3 - Plant the tank (more than you think)

Add plants before filling.

Heavily planted tanks:

• Reduce stress
• Help water quality
• Create natural resting places

Attach Anubias/Java fern to wood or rocks. Plant crypts into the substrate.

Step 4 - Fill with water and add dechlorinator

• Fill slowly to avoid disturbing the substrate
• Add water conditioner for the full tank volume
• UK tap water always needs treatment (chlorine/chloramine)

Tip: Pour water onto a plate or plastic bag to avoid uprooting plants.

Step 5 - Start the heater and filter

• Set the heater to 25–26°C
• Ensure filter flow is gentle
• Place the thermometer where you can see it easily

Let the tank run for 24 hours to stabilise the temperature before continuing.

Step 6 - Set a simple light schedule

6–8 hours per day is enough.

Too much light = algae.
Too little = poor plant growth.

Use a timer if possible.

Step 7 - Begin the fishless cycle (do not add the betta yet)

This is where patience matters.

Start testing the water over the next few weeks and allow beneficial bacteria to establish before adding your fish.

Skipping this step is the number one reason betta tanks fail.

Fishless Cycling Made Simple (UK): The Part Most Guides Rush

Cycling is not about “letting the tank sit”.

It’s about growing beneficial bacteria that make the water safe for your betta.

In UK homes, where room temperatures are cooler, this process often takes longer than guides suggest. That’s normal.

Patience here prevents nearly all beginner problems later.

What to test (and why)

You only need to monitor three things:

Use a liquid test kit every 2–3 days.

Typical timeline in a 20–40L UK tank

Cooler rooms = slower bacteria growth. This is normal.

What you actually do during this time

• Keep the heater at 25–26°C
• Keep the filter running 24/7
• Add a small ammonia source (fish food or bottled ammonia)
• Test every few days
• Do nothing else

No water changes unless levels go extremely high.

When can you safely add your betta?

Only when:

• Ammonia = 0
• Nitrite = 0
• Nitrate is present

That’s the signal that the tank can safely process waste.

The mistake most beginners make:

They think clear water means safe water. It doesn’t. Only testing tells you when the tank is ready.

Adding Your Betta: Acclimation + First 7 Days

This is the moment most beginners worry about.
If the tank is cycled, this part is simple and calm, especially if you already know the right betta feeding schedule and food choices for the first days.

Acclimation (don’t rush this)

1. Float the sealed bag in the tank for 15–20 minutes to match the temperature.
2. Open the bag and add a small amount of tank water every 5 minutes (3–4 times).
3. Gently release the betta into the tank.
4. Leave the lights off for a few hours.

This reduces stress and prevents shock.

What to expect in the first hours

Your betta may:

• Hide
• Explore slowly
• Rest near plants or the surface

This is normal.

First 7 days checklist

Signs everything is going well

• Betta swims calmly
• Uses plants and hides
• Comes to the front when you approach
• Eats normally after day 2

Signs of stress to watch for

• Gasping at the surface constantly
• Hiding all day
• Clamped fins
• Not eating after 2–3 days

These usually point to water quality or strong flow.

Betta Tank Setup Ideas: 3 Layouts That Work Perfectly in 20–40L

Common Mistakes to Avoid (UK Beginner Edition)

Most betta problems don’t come from bad intentions; they come from following generic advice that doesn’t work well in UK homes.

Here are the mistakes that cause most issues in the first month.

Using 10L nano kits sold as “betta tanks”

These tanks are too small to stay stable:

• The temperature drops quickly at night
• Water quality changes fast
• Filters are often too strong and not adjustable

This is the number one reason beginners think bettas are “difficult”.

Not using a heater

The room temperature is not warm enough in the UK.

Without a heater, water often drops below 22°C at night, stressing the betta even if the tank looks fine.

Strong filter current

If the betta is constantly fighting the flow, it will:

• Hide
• Become lethargic
• Develop torn fins

Filtration should be gentle, not powerful.

No lid on the tank

A lid:

• Prevents cold air exposure
• Reduces evaporation
• Stops jumping

In UK homes, this matters more than most people realise.

Overfeeding in the first days

Extra food = extra waste = ammonia spike in new tanks.

Feed less than you think. A hungry betta is safer than an overfed one.

Skipping the cycling process

Clear water does not mean safe water.

Only a completed nitrogen cycle makes the tank safe for a betta. Testing is the only way to know.

FAQ

What is the ideal setup for a betta fish?

A 20–40L tank with a heater set to 25–26°C, a low-flow filter, a lid, live plants, and fully cycled water.

This combination keeps the water stable, reduces stress, and creates the calm environment bettas need to thrive in UK homes.

What do bettas need in their tank?

Warm, stable water, gentle filtration, places to hide and rest near the surface, and clean, cycled water.

Bettas don’t need large tanks or strong equipment; they need stability and calm conditions.

How long before you can put a betta in a new tank?

Usually 4–6 weeks, once the fishless cycle is complete.

You can safely add a betta only when ammonia and nitrite read 0 and nitrates are present.

Do bettas need oxygen or an air pump?

No. Bettas breathe from the surface using their labyrinth organ.

An air pump is only needed when using a sponge filter or if you want extra surface agitation.

Betta tank setup with plants, do I still need a filter?

Yes. Plants help improve water quality, but they cannot replace biological filtration.

A gentle filter is still required to keep the water safe long-term.

Betta tank setup UK, what about hard water?

Most bettas adapt well to UK tap water.

Chasing perfect numbers is less important than keeping temperature, filtration, and maintenance stable.

Conclusion

A proper betta setup in the UK is not about expensive gear or tiny kits marketed for convenience.

It’s about getting a few fundamentals right:

• Enough water (20–40L)
• Stable warmth (25–26°C)
• Gentle, low-flow filtration
• Plants and cover for security
• Patience to cycle the tank properly

Once these are in place, keeping a betta becomes simple, calm, and enjoyable.

If you’re still deciding on tank size, the Betta Tank Size UK guide will help you choose the right volume.
If you’re new to bettas, the Betta Fish UK care guide explains feeding, behaviour, and long-term care.
And if you’re tempted by small kits, read the 10L tank reality check first.

Do this once, do it right, and your betta can thrive for years. 

At AquaticsHub, we focus on practical, modern, welfare-first aquarium setups that actually work in UK homes, not marketing kits that look good on shelves but create problems later.

That’s why this guide exists.