By Kevin
Every week we get the same message: "I want to start a tropical fish tank and I have no idea where to begin." This is the page we'd hand them. I'm Kevin, the editor here, and after years of answering "which fish first?" emails, I've learned the question behind the question is never really about fish — it's about confidence. People want to know they won't kill the thing they just bought.
So this guide does two things. First, it answers what "tropical fish" actually means, because that one word covers thousands of species and a lot of bad advice. Second, it walks you through the decision every beginner faces: which tropical fish should be your first, and what they need to thrive. If you want the deeper buying shortlist, our best beginner tropical fish guide ranks ten species in detail; this page is the wider map.
Tropical fish are warm-water freshwater species — they need a heater holding 24–26 °C. That's the line that separates them from coldwater fish (goldfish, which want 18–22 °C) and marine fish (saltwater). Most of England's tap water is hard [5], which happens to suit livebearers beautifully. You're not fighting your tap water from day one if you start with the right species.
What counts as a "tropical fish"?
"Tropical fish" isn't a scientific group — it's a hobby term for freshwater fish from warm parts of the world that we keep in a heated aquarium. They fall into a handful of familiar families:
- Livebearers (guppies, platies, mollies, swordtails) — they give birth to live young rather than laying eggs, and they're the hardiest starting point for UK water.
- Tetras and rasboras (neon tetra, cardinal, harlequin) — small schooling fish that move together through the middle of the tank.
- Catfish (corydoras, bristlenose) — bottom-dwellers that sift the substrate and graze algae.
- Danios (pearl danio, zebra danio) — fast, active schoolers that tolerate a wide temperature range.
- Gouramis and small cichlids (honey and dwarf gourami, angelfish) — larger "centrepiece" fish with personality.
The featured species further down this page deliberately span all five families, because a good first tank usually has one of each role rather than five of the same thing. If you want to browse the whole range, our tropical fish for sale hub is the full shop, and the community tank fish hub filters to species that get along.
Tropical vs coldwater vs marine — which one are you starting?
The single most common mix-up we untangle on email is "tropical or coldwater?" — and it matters, because the equipment and the fish are not interchangeable. Here's the honest comparison:
| Tropical freshwater | Coldwater freshwater | Marine (saltwater) | |
|---|---|---|---|
| Typical temperature | 24–26 °C | 18–22 °C | 24–26 °C |
| Heater needed? | Yes | No (room temp) | Yes |
| Example fish | Guppy, tetra, corydoras | Goldfish, white cloud | Clownfish, tangs |
| Water cost | Tap water (UK water often ideal) | Tap water | RO + marine salt mix |
| Beginner cost + effort | Low–moderate | Low–moderate | High |
| Best for a first tank? | Yes | Goldfish need big tanks | No — start freshwater |
Tropical freshwater is the sweet spot for almost every first-timer: the fish are colourful and varied, the kit is affordable, and UK tap water suits the hardiest species without any treatment. Goldfish look "easy" but are messy and outgrow small tanks fast. Marine is a wonderful hobby — but it's a second or third tank, not a first.
It's tempting to put a goldfish in with tropical fish, but their temperature needs barely overlap and goldfish produce far more waste. Pick one world and build the tank around it. This page is about the tropical freshwater route — the one we'd recommend to start.
Five facts most UK tropical-fish guides skip
- The neon tetra tops 'is your tank ready?' more than any other fish. It's the species most beginners lose in a brand-new tank, because it's sensitive to the parameter swings of water under six to eight weeks old [3]. Add neons to a mature tank.
- An adult neon tetra is barely 2.5 cm long. FishBase lists a maximum standard length of 2.5 cm [1] — which is exactly why you keep them in a group of ten or more. One or two simply vanish in the tank.
- You're growing bacteria, not just adding water. "Cycling" means building colonies of nitrifying bacteria that convert toxic ammonia to nitrite and then to far-less-toxic nitrate. Ammonia and nitrite are recognised as major stressors to aquatic animals [2] — which is why a fish-in, uncycled tank is the classic beginner killer.
- UK tap water is a gift if you pick the right fish. Most of South-East England is supplied with hard water from chalk and limestone [5]. Livebearers evolved for exactly that — so guppies, platies and mollies thrive straight out of the tap with no remineralising kit.
- "Common pleco" is the most mis-sold fish in the trade. It's often sold at 5 cm for a small tank, then grows to around 40 cm and needs a tank of 400 litres or more. Always check the adult size before you buy — the gold suckermouth catfish further down this page is a deliberate cautionary example.
The most popular beginner tropical fish
Here's the shortlist we'd actually point a first-time keeper at — a diverse spread across livebearers, schoolers, catfish and centrepieces. Every one of these is a real species we stock, and the beginner rating reflects how forgiving it is in a typical cycled UK community tank.
| Species (our name) | Type | Adult size | Temperament | Beginner rating |
|---|---|---|---|---|
| Neon Tetra | Tetra (schooler) | ~4 cm | Peaceful | Easy (mature tank) |
| Female Guppy | Livebearer | ~6 cm | Peaceful | Very easy |
| Assorted Variatus Platy | Livebearer | 5–6 cm | Peaceful | Very easy |
| Swordtail Marry Gold | Livebearer | ~5 cm | Semi-active | Easy |
| Assorted Balloon Molly | Livebearer | 8–10 cm | Peaceful | Easy (needs space) |
| Pearl Danio | Danio (schooler) | ~5.5 cm | Peaceful, active | Easy |
| Panda Cory | Catfish (bottom) | ~5 cm | Peaceful | Easy (keep in groups) |
| Neocaridina Shrimp | Invertebrate | ~3 cm | Peaceful | Easy (clean-up crew) |
| Bristle Nose Catfish | Catfish (algae) | up to 15 cm | Peaceful | Easy (90 L+) |
| Female Dwarf Gourami | Gourami (centrepiece) | ~9 cm | Peaceful | Easy–moderate |
| Angel Fish Small | Cichlid (centrepiece) | up to 15 cm | Semi-aggressive | Intermediate |
| Suckermouth Catfish Gold | Catfish (common pleco) | up to 40 cm | Peaceful | Advanced — large tank only |
Read this table top to bottom as a difficulty gradient. The livebearers and pearl danio are where a first-timer should start. The angelfish and gold suckermouth are real fish people buy as beginners and shouldn't — they're on the list so you can recognise the trap.
How to choose your first tropical fish
The mistake isn't picking the "wrong" fish — it's picking fish that don't match the tank and water you actually have. Work through these four questions in order:
- How big is your tank? A cycled 60 L holds a sensible small community; 90 L is more forgiving and opens up more species. Avoid 20–30 L kits for a first community — they swing in temperature and chemistry too fast [4].
- How hard is your water? Most UK tap water is medium-to-hard [5]. That's perfect for livebearers and most South American tetras, and uncomfortable for soft-water specialists. Start with what your tap gives you.
- What's the adult size? A fish sold at 4 cm might stay 4 cm — or hit 40. Check before you buy. The gold suckermouth catfish in the table is a 40 cm fish; the bristlenose is the sensible small alternative.
- Is it a schooling fish? Tetras, rasboras, danios and corydoras must live in groups of six or more. Kept singly they hide, stress and die young. Plan the group size into your stocking before you order.
A strong first community usually has: one schooling group (a danio or tetra shoal), one or two livebearer species, one bottom group (corydoras), and maybe one gentle centrepiece (a dwarf gourami). That's far easier to manage — and nicer to watch — than a tank with one of everything.
Starter tank size, heater and cycling
Three non-negotiables before any fish goes in:
- Tank: 60 L minimum for a community, 90 L if you have the room.
- Heater: every tropical fish needs one. 50 W for 60 L, 100 W for 90–120 L, set to 24–26 °C.
- Cycle: run the filter and heater fishless for 4–6 weeks until ammonia and nitrite both read 0 within a day of dosing. Skipping this is the number-one reason first tanks fail [2]. Our first tropical tank guide walks the whole cycle through step by step.
Building a community tank
The phrase "community tank" just means a mix of peaceful fish of similar size that live happily together [4]. The art is in the balance, not the headcount. Picture the tank in three layers:
- Top and mid-water: a livebearer group (guppies, platies, swordtails) plus a schooling shoal (pearl danios, then neon tetras once mature).
- Bottom: a group of panda corydoras — peaceful catfish that work the substrate all day. Keep them on smooth gravel or sand so they don't wear down their barbels.
- Clean-up + feature: a bristlenose catfish to graze algae, a colony of Neocaridina shrimp, and optionally one gentle centrepiece such as a female dwarf gourami.
For the detail on each species, our care guides go deep: guppy care, neon tetra care, platy care, molly care, corydoras care and honey gourami care. And before you stock anything, the water chemistry guide explains the pH and hardness numbers in the key-facts table above.
Angelfish are sold small and look easy, but they reach 15 cm, want a 150 L tank, turn territorial as adults, and will eat small tetras. The common (gold suckermouth) pleco grows to around 40 cm and needs 400 L+. Both are wonderful fish — for a second, much larger tank. Neither is a true first fish. Choose a bristlenose for algae and a dwarf gourami for a centrepiece instead.
We do stock both, and they're brilliant fish in the right home — so if you're planning a larger tank down the line, bookmark them rather than buying for a first 60 L:
What mixes well — a quick compatibility guide
Most of the species on this page are peaceful and combine freely. The few cautions are about size and temperament, not aggression for its own sake:
| Species | Mixes with | Watch out for |
|---|---|---|
| Guppy / platy / swordtail | Tetras, danios, corydoras, shrimp | Fin-nippers; very large fish |
| Neon tetra / pearl danio | Livebearers, corydoras, gourami | Big-mouthed fish that see them as food |
| Panda corydoras | Everything peaceful | Sharp gravel wears their barbels |
| Neocaridina shrimp | Small peaceful fish, snails | Larger hungry fish will eat them |
| Bristlenose catfish | Whole community | Needs driftwood; one per small tank |
| Female dwarf gourami | Calm community | Boisterous tank mates stress them |
| Angelfish (adult) | Larger peaceful fish | Eats neon-sized fish; territorial |
The pattern is simple: keep everyone roughly the same size, give schooling fish their groups, and don't house bite-sized fish with mouths big enough to swallow them. Our community tank fish hub is pre-filtered to species that follow exactly these rules.
Watch: setting up a simple tropical tank
Before you spend anything, it helps to see the setup done from scratch. This short clip shows the rhythm of a calm community tank — the end goal you're aiming at.
When your tropical fish arrive
We ship live fish with a licensed live-animal courier, so they reach you quickly and warm. The acclimation routine is the same gentle drip for all the community species on this page — the difference is mostly patience:
- Receive in a quiet room, lights dimmed. Check the bag is warm, not cold.
- Float the sealed bag in the tank for 15–20 minutes so temperatures equalise.
- Drip-acclimate for 30–40 minutes at one to two drops a second. Hardy livebearers cope with 30 minutes; smaller, more sensitive fish like neon tetras prefer the longer end [6].
- Net, don't pour — lift the fish into the tank with a net and discard the bag water.
- Lights off for a couple of hours, and no feeding for 24 hours so they settle.
Even with a fully cycled tank, add one group, wait a week or two, test the water, then add the next. The filter needs time to scale its bacteria to each jump in waste. Most "my new fish died" stories come from adding everything in a single shop.
What can go wrong in the first month — and what to do
Most beginner problems are not mysterious diseases. They're water-quality issues with a handful of recognisable signs. Almost all of them trace back to the same root cause: an immature filter, too much food, or too many fish too fast [2]. Use this as a quick triage chart:
| Symptom | Most likely cause | What to do first |
|---|---|---|
| Fish gasping at the surface | Ammonia or nitrite spike (uncycled / overfed) | Test water; 25–50% water change; stop feeding for 48 h |
| Cloudy white water in a new tank | Bacterial bloom — normal early in cycling | Don't add fish yet; keep filtering; it clears in days |
| New fish dies within days | Added to an uncycled or unstable tank | Confirm the cycle is complete before restocking |
| Fish hiding, clamped fins, dull colour | Stress from poor water or wrong parameters | Test water; check temperature is steady at 24–26 °C |
| Green water or algae on glass | Too much light + nutrients | Reduce lighting hours; add a bristlenose; less food |
| One fish chasing others relentlessly | Overstocked, or a semi-aggressive species | Re-check stocking; rehome or separate the aggressor |
Nine times out of ten, the underlying problem is the tank was stocked before it finished cycling, or it's being fed too heavily. A test kit is the cheapest insurance you can buy — knowing your ammonia, nitrite and nitrate readings turns guesswork into a clear next step. Feed only what the fish finish in a minute, twice a day, and you'll avoid most of this list entirely.
What does it cost to start?
A realistic budget helps more than a wish list. Tropical fishkeeping is affordable to start and cheap to run — the fish themselves are usually the smallest line:
- The fish: most hardy community species are £2–£7 each. A first stocking of 15–20 fish is roughly £40–£90.
- The tank, heater and filter: the bulk of the up-front cost, and a one-off. A 60–90 L setup is the sweet spot.
- Running costs: a heater and small filter draw little power; food and the occasional water-test kit are pennies a week.
Because livebearers breed, a small starting group of guppies or platies often grows into more fish at no extra cost — one reason they're such good value for a first tank. Spend the money on the right tank size and a proper cycle; the fish are the easy part.
Related reading
Close the loop — here's where to go next:
- Shop: tropical fish for sale, community tank fish
- Learn: first tropical tank guide, water chemistry basics
- Compare: best beginner tropical fish — top 10, tropical fish for sale in the UK
If you'd like a second pair of eyes on your stocking plan — tank size, species mix, water parameters — send us the details before you order. We'd far rather spend ten minutes on email than ship fish into a tank that won't suit them.
