Guide
Aquarium keeping in the UK
Litres and gallons, hard water, retail, and what British hobbyists need to know.
- Units: UK tanks are sized in litres. US guides use US gallons (1 US gal = 3.78 L); older UK products may reference imperial gallons (1 imp gal = 4.55 L). Always check which gallon is being used.
- Tap water: Most of the UK - especially the South and East of England - has hard, alkaline water. Choose fish accordingly or invest in RO or softening equipment.
- Where to buy: Pets at Home is convenient; Maidenhead Aquatics offers more variety; independent aquatics specialists are often your best source of advice and healthy stock.
- Legal requirement: Never release aquarium fish, invertebrates, or plants into the wild. It is a criminal offence under UK law, and several common aquarium species are on the invasive species banned list.
- New keeper priority: Cycle your tank before adding fish. This single step prevents more deaths than anything else in the hobby.
Litres, imperial gallons, and US gallons - getting the units right
UK aquarium retail runs on litres, and that is what tank manufacturers print on the box. A 120-litre tank is a typical starter size; serious community tanks start around 200 litres; anything under 60 litres is genuinely difficult to keep stable and should be treated with caution regardless of what marketing says about it being "perfect for beginners."
The confusion comes when you use American fishkeeping resources - YouTube channels, Reddit, US-based care sheets - because they work in US gallons. One US gallon is 3.78 litres. One imperial gallon (still referenced in older UK books and some product labels) is 4.55 litres. That difference matters when you are dosing dechlorinator, calculating stocking, or sizing a heater.
A quick rule: if a US guide says a fish needs a 20-gallon tank, that is roughly 75 litres minimum. If it says 55 gallons, you are looking at around 208 litres. Always check the source before you trust a gallon figure - a US "10-gallon nano" is only 38 litres, not the 45-litre tank that number suggests to a UK reader used to imperial.
Dosing bottles for dechlorinator, plant fertilisers, and medications in the UK are calibrated per litre. Never apply US dosing rates (per US gallon) without converting - you will either underdose or, with medications, risk overdosing and harming your fish.
Hard water: the defining challenge of UK fishkeeping
If you live in London, the Home Counties, East Anglia, the Midlands, or much of the South, your tap water is hard - sometimes very hard. Thames Water, for instance, delivers water with a GH regularly above 15 °dH and a pH of 7.5-8.2 straight from the tap. This is not a problem; it is just reality, and it shapes every stocking decision you make.
Fish that thrive in hard, alkaline UK tap water
The good news: a huge range of popular fish love exactly this water chemistry. Livebearers - guppies, platies, mollies, swordtails - originate from hard, mineral-rich Central American rivers and do better in UK tap water than they would in soft water. African cichlids from Lakes Malawi and Tanganyika (Rift Valley cichlids like Pseudotropheus spp. or Neolamprologus spp.) actively need high pH and hardness. Many rainbowfish, goldfish, and most shell-dwelling cichlids are equally well-suited.
Fish that struggle without water treatment
Soft-water species are where hard tap water causes genuine problems. Discus (Symphysodon spp.) need soft, acidic water (pH 6.0-7.0, GH under 8 °dH) to breed and usually to stay healthy long-term. Many South American tetras - rummy-nose (Hemigrammus bleheri), cardinal (Paracheirodon axelrodi) - do best in softer, more acidic conditions, though they tolerate moderately hard water better than their reputation suggests. Apistogramma dwarf cichlids and wild-caught Betta varieties also prefer softer water.
If you want to keep these species seriously, you have two realistic options: a reverse osmosis (RO) unit, which strips minerals out and lets you build water chemistry from scratch using remineralising salts, or a water softener - though note that ion-exchange softeners replace calcium and magnesium with sodium, which is not ideal for fish. RO is the better long-term solution for soft-water tanks.
Buying discus or wild-type cardinal tetras because they look spectacular, then trying to keep them in untreated South East England tap water. The fish rarely thrive, the keeper gets frustrated, and the fish die. Check your tap water hardness before you buy anything, not after.
How to find out what comes out of your tap
Your water company is legally required to publish annual water quality reports online - search "[your supplier] water quality report" and look for GH, KH, or total hardness in mg/L CaCO₃ (divide by 17.8 to get °dH). Better still, buy a liquid test kit (API or JBL) and measure it yourself, because hardness can vary by postcode even within a single water company's supply area. You should also measure pH: UK tap water typically runs pH 7.0-8.0 depending on your area and the time of year.
Always treat tap water with a dechlorinator before adding it to your tank. UK water is treated with chlorine or chloramine; both are lethal to fish and the beneficial bacteria in your filter. Sodium thiosulphate-based dechlorinators handle chlorine; products like Seachem Prime also neutralise chloramine.
Where to buy fish and equipment in the UK
Pets at Home is the dominant chain and it is fine for basic equipment, food, and hardy beginner species. Staff quality varies considerably between branches. Their live fish sections have improved, but livestock choice is limited and you will not find anything unusual there.
Maidenhead Aquatics, often co-located in garden centres (Wyevale, Squire's, and others), is a specialist aquatics retailer with significantly wider livestock choice and generally more knowledgeable staff. Worth the extra trip for sourcing specific species or getting a second opinion on a problem.
Independent aquatics shops are where the serious hobby lives. They are harder to find, sometimes inconveniently located, and occasionally look like they have not been decorated since 1987 - but the stock is usually better conditioned, the advice is more reliable, and you will find species the chains never stock. Find your nearest via local fishkeeping clubs or the OATA's retailer directory.
Pets at Home will sell you a 30-litre tank and tell you it is suitable for a community of fish. It is not. A 30-litre tank with a standard internal filter is suitable for a single Betta or a small colony of shrimp. If a shop recommends stocking levels that do not add up, check them yourself using a free stocking calculator before you buy.
Online retailers
Buying fish online in the UK is a real and widely-used option. Retailers like Aquacadabra, Swell UK, and SwissTropicals ship livestock via next-day courier in insulated boxes. Fish arrive stressed but usually recover well if your tank is properly cycled and the water temperature matches. Read reviews, check the live arrival guarantee, and never order livestock if a heatwave or hard freeze is forecast.
Clubs and forums
The Federation of British Aquatic Societies (FBAS) coordinates local fishkeeping clubs across the UK. These are worth joining: you get access to fish auctions (often the only way to find unusual or locally-bred species at sensible prices), free advice from experienced keepers, and usually someone who can take fish off your hands when you need to rehome them. Online, the Tropical Fish Forums and UK Aquatic Plant Society communities are active and knowledgeable.
UK regulations: what you legally need to know
This is the section most guides skip over and it genuinely matters.
Invasive non-native species
It is a criminal offence under the Wildlife and Countryside Act 1981 (and subsequent amendments) to release non-native species into the wild in the UK. This includes aquarium fish, aquatic invertebrates, and plants. The offence applies whether you are releasing unwanted fish into a local pond, dumping aquarium water containing eggs or plant fragments into a drain that leads to a waterway, or disposing of live plants irresponsibly.
Several common aquarium plants are specifically listed under the UK's Invasive Non-Native Species regulations and cannot legally be sold, kept with intent to release, or allowed to spread: these include Hydrocotyle ranunculoides (floating pennywort), Ludwigia grandiflora, and Myriophyllum aquaticum (parrot's feather). Some of these are still occasionally sold in garden centres by mistake - ignorance is not a defence.
If you need to dispose of aquarium plants, seal them in a bag and put them in your household waste bin. If you need to rehome fish, contact a local club, aquatics shop, or use online rehoming groups. Do not put them in a pond or waterway, ever.
Water from your aquarium can contain fish eggs, plant fragments, snail eggs, and microscopic organisms. Do not empty tank water into a garden that drains to a stream or river. Pour it on non-draining beds, compost it, or dispose of it down the household drain.
Post-Brexit import rules
Since 2021, live fish and aquatic plants imported from the EU are subject to UK Border Force biosecurity checks and require health certificates. This has increased costs and complexity for specialist importers, which is one reason some unusual species are harder to source and more expensive in the UK than they were before 2021. Reputable retailers absorb this into their compliance processes; if a seller is offering suspiciously cheap, recently imported livestock with no paperwork, that is a red flag.
DEFRA publishes current rules on importing live aquatic animals; if you are bringing fish back from a holiday or importing directly from an overseas breeder, check the current CITES and DEFRA requirements before you do anything.
Setting up a tank in the UK: practical starting points
The fundamentals of fishkeeping are the same everywhere, but a few things are worth calling out specifically for UK conditions.
Cycle your tank first. This cannot be overstated. The nitrogen cycle needs to establish before fish go in, and rushing it is the single most common cause of fish deaths in new tanks. Expect four to eight weeks for a fishless cycle. Understand what you are testing for - ammonia, nitrite, nitrate - before you add anything living.
UK electricity and equipment. UK mains is 230 V / 50 Hz. Most aquarium equipment sold in the UK is pre-wired for this. If you buy equipment from the US or Asia (common via eBay or Amazon Marketplace), check the voltage rating. A 110 V US heater plugged into a UK socket will fail immediately or be a fire hazard.
Water temperature and room temperature. UK homes are generally cool, especially in winter. A heater is necessary for tropical fish in virtually all UK households - even a "warm" living room in January sits at 18-20 °C, well below the 24-28 °C most tropical species need. Size your heater at approximately 1 watt per litre as a baseline, but go larger if your room gets cold overnight.
For beginner-friendly species that work well with hard UK tap water, consider starting with platies, white cloud mountain minnows (Tanichthys albonubes, which can even be kept unheated in a cool room), or a group of zebra danios (Danio rerio). All are hardy, forgiving, and widely available.
Track your parameters and get care reminders with App-aquatic.
Get the free appIs UK tap water safe for fish after using dechlorinator?
For hard-water species, yes - dechlorinate with a product that also neutralises chloramine (Seachem Prime, NT Labs Tapsafe Plus, or similar), and you are good. For soft-water species like discus or wild-type cardinal tetras, UK tap water in most areas is too hard even after dechlorination; you will need RO water blended to the right parameters.
Which is better: Pets at Home or Maidenhead Aquatics?
For equipment and basics, either works. For livestock quality and species variety, Maidenhead Aquatics is generally the better option. For genuine expertise and unusual stock, find a good independent specialist - they are worth the extra journey.
Can I keep a pond fish (like a common goldfish) in an indoor tank?
Not long-term. Common goldfish grow to 30 cm or more and produce a heavy waste load. They need large, well-filtered tanks or ponds. A 20-litre starter tank will stunt and eventually kill a common goldfish. Fancy goldfish varieties (Oranda, Ryukin) are smaller and more manageable but still need 120+ litres for a pair.
What aquarium plants are illegal in the UK?
Floating pennywort (Hydrocotyle ranunculoides), parrot's feather (Myriophyllum aquaticum), and Ludwigia grandiflora are among the species listed under the UK's invasive non-native species schedule. They cannot legally be sold or released. Some other species are restricted - check the full DEFRA/NatureScot list before buying unfamiliar aquatic plants.
How do I find a local fishkeeping club in the UK?
The Federation of British Aquatic Societies (FBAS) maintains a directory of affiliated clubs at fbas.co.uk. Most clubs run monthly meetings with talks, fish auctions, and plant swaps - they are one of the best ways to access species you will never see in a shop and to get honest advice from experienced keepers in your local water area.
More guides · Tap water · Water parameters · USA guide · Canada guide · Australia guide · App-aquatic