Guide
What is a good beginner setup for coldwater? The complete guide
No heater. That’s the main appeal of a coldwater tank — and it’s a genuine benefit. But “no heater” doesn’t mean “no work.” Coldwater fish still need filtration, a cycled tank, appropriate space, and compatible species. This guide tells you exactly what to do, what to buy, and what fish will actually thrive.
- Best beginner fish: White Cloud Mountain Minnows — beautiful, hardy, active, 60L+ tank.
- Best alternative: Weather Loach — character fish, very hardy, 100L+.
- Goldfish? Great long-term fish, but they need proper space (150L+ for two fancy goldfish) and excellent filtration. Not the "easy" starter fish you were told.
- What you always need: Filter, test kit, dechlorinator, thermometer. No heater, but everything else still applies.
- What to avoid: Bowls. Small tanks for large fish. Single-tail goldfish in indoor tanks. Mixing with tropical fish.
What counts as a coldwater fish tank?
A coldwater aquarium is one kept at ambient room temperature — no heater required. In practice in the UK, this means a tank operating in the range of 14–22°C depending on the season and your home’s central heating. This suits fish that come from temperate climates: rivers, streams, and ponds of East Asia, Europe, and North America, where water is cool to cold.
This is distinct from:
- Tropical tanks (24–28°C) — which need a heater to maintain temperature.
- Pond keeping — outdoor ponds operate at ambient outdoor temperature, going genuinely cold (below 10°C) in winter, which most indoor coldwater fish cannot handle long-term.
The “coldwater” label also comes with a warning: if your home gets genuinely hot in summer (above 24–25°C), your coldwater tank can become uncomfortably warm for fish that prefer 18°C. Unlike cold, which you manage with a heater, heat requires different management — fans over the water surface, turning off lights during peak heat, or moving the tank to a cooler location.
The equipment you actually need
Here’s the honest list — no heater, but everything else is the same as a tropical setup:
- Tank: Appropriately sized for your chosen fish (see fish sections below). Bigger is better — larger water volume means more stable parameters.
- Filter: Non-negotiable. Biological, mechanical, and ideally chemical filtration. Sized for your tank — err on the larger side.
- Thermometer: Essential even without a heater — you need to know if your room is too warm in summer.
- Test kit: API Master Test Kit or equivalent. Test ammonia, nitrite, nitrate, and pH. A test kit is not optional — it's the only way to know if your tank is safe.
- Dechlorinator: Tap water contains chlorine and chloramine — both lethal to fish. Treat every water change.
- Substrate: Fine gravel or sand. Smooth edged — particularly important for bottom dwellers like loaches.
- Plants (optional but highly recommended): Live plants improve water quality, provide hiding spots, and make the tank look better. Coldwater-tolerant: java fern, anubias, hornwort, vallisneria.
- Lid: Coldwater fish — particularly weather loach and some minnows — are escape artists. A lid is essential.
Skipping the cycling process because “it’s just a coldwater tank.” The nitrogen cycle operates exactly the same way in coldwater tanks. Beneficial bacteria that process fish waste (ammonia → nitrite → nitrate) grow slightly slower in cooler water — which means cycling can actually take longer in a coldwater tank than a tropical one, not shorter. Adding fish to an uncycled tank causes toxic ammonia buildup regardless of temperature. Cycle first, add fish after. Always.
The best coldwater fish for beginners
1. White Cloud Mountain Minnow (Tanichthys albonubes) — top recommendation
The White Cloud Mountain Minnow is the best beginner coldwater fish in the hobby, full stop. Here’s why:
- Temperature range: 14–22°C (can briefly tolerate 8–28°C). Genuinely cold-tolerant — they’re named after White Cloud Mountain in China where mountain streams are cold year-round.
- Size: 3–4 cm — small, school-oriented, suitable for smaller tanks.
- Minimum tank: 60 litres for a school of 8–10.
- Hardiness: Excellent. Tolerates a wide pH range (6.0–8.0), moderate hardness, and is genuinely forgiving of beginner mistakes compared to many fish.
- Appearance: Surprisingly striking — metallic gold lateral stripe, red-tipped fins. Schooling behaviour when numerous looks spectacular.
- Compatibility: Peaceful, suitable with other small coldwater fish. Do not mix with goldfish — goldfish will eat them.
If someone asks you “what fish should I get for my first coldwater tank?” — White Cloud Mountain Minnows, in a school of at least 8, in a 60L+ planted tank. That’s the answer.
White Clouds are a schooling fish and display natural behaviour — active swimming in formation, vibrant colour display — only in groups. Fewer than 6 individuals causes stress and hiding behaviour. A school of 8–10 in a 60–80L planted tank is one of the most rewarding and low-maintenance coldwater setups available to beginners.
2. Weather Loach / Dojo Loach (Misgurnus anguillicaudatus)
The Weather Loach is a serious character fish that gets unfairly overlooked in favour of trendier species.
- Temperature range: 5–25°C — genuinely coldwater-tolerant through to subtropical.
- Size: 20–30 cm at maturity. They grow. A “cute small loach” from the shop becomes a substantial fish.
- Minimum tank: 100+ litres for a pair.
- Behaviour: Highly active, social, and entertaining. They are named “weather loach” because they become hyperactive when air pressure changes before storms — widely observed by keepers. They also readily eat from your hand and become recognisably interactive with familiar people.
- Substrate: Must have soft sand or fine smooth gravel — they burrow and rest on the substrate. Sharp gravel damages their barbels and underbelly.
- Escape risk: High. A tight-fitting lid is essential — they can squeeze through remarkably small gaps.
3. Hillstream Loach (Sewellia, Beaufortia, Gastromyzon species)
Hillstream loaches are fascinatingly bizarre — flattened like a miniature ray, adapted to cling to surfaces in fast-flowing rocky mountain streams. They are algae and biofilm grazers rather than conventional fish in their behaviour.
- Temperature range: 16–24°C (prefer cool, well-oxygenated water).
- Size: 5–8 cm depending on species.
- Minimum tank: 80L minimum, but water flow is the critical variable — they need high flow and excellent oxygenation. A powerhead or wavemaker alongside the main filter is strongly recommended.
- Diet: Biofilm, algae, and algae wafers. They graze constantly. A mature tank with algae growth on glass and rocks is ideal. Supplement with algae wafers and blanched vegetables.
- Note: Hillstream loaches are not beginner fish despite being coldwater — they have specific oxygenation and flow requirements that beginners sometimes underestimate. Establish a mature, heavily planted tank with strong flow before adding them.
4. Goldfish — the honest assessment
Goldfish are the default answer to “what should I put in my coldwater tank?” and they are genuinely great fish — when kept correctly. The problem is that “kept correctly” is very different from how they are typically sold and kept by beginners.
Goldfish are easy beginners' fish. A small tank or bowl is fine to start. They'll be happy in whatever you give them. They stay small. They're low maintenance.
Goldfish are high-bioload fish that produce extreme amounts of waste. Fancy goldfish grow to 15–20 cm. Single-tail (common/comet) goldfish can reach 30–45 cm. They need powerful filtration, a large tank (150L minimum for two fancy goldfish), and regular substantial water changes. Bowl-kept goldfish die early from ammonia poisoning and oxygen deprivation — not because goldfish are fragile, but because they're kept in entirely unsuitable conditions.
If you want goldfish — fantastic choice. Set it up properly:
- Tank size: 150L minimum for two fancy goldfish (oranda, ryukin, black moor, etc.). Add 40–50L per additional fancy goldfish. Single-tail goldfish (comet, common) grow very large — a pond is their appropriate home; a 200L+ tank is the minimum for a single adult.
- Filtration: Oversized. A filter rated for 300L in a 150L goldfish tank is not excessive — goldfish produce significantly more waste than most fish of equivalent size.
- Water changes: 25–30% weekly minimum. The waste load in a goldfish tank means water quality degrades faster than in most other setups.
- Temperature: Goldfish prefer 16–22°C. They tolerate 10–24°C. They struggle above 26°C. Like coldwater fish generally, summer heat management is sometimes needed.
- Companions: Goldfish should be kept only with other goldfish of similar size and type. Fancy goldfish with single-tail goldfish causes problems — the faster-moving single-tails outcompete the slower fancy varieties for food. Do not mix with tropical fish or small fish that goldfish will eat.
5. Paradise Fish (Macropodus opercularis)
An underrated choice — a labyrinth fish (related to bettas and gouramis) that tolerates temperatures as low as 15°C. Males are striking: vivid red and blue striped bodies with long flowing fins. Like bettas, males are aggressive toward each other and cannot be kept together. But a single male Paradise Fish in a 60–80L coldwater tank with a school of White Cloud Mountain Minnows is a beautiful and unusual combination that few people consider.
Species to avoid in coldwater setups
- Tropical fish: Do not put neon tetras, bettas, or any fish labelled as tropical in a coldwater tank. The temperature differential causes chronic immune suppression and early death.
- Common/comet goldfish in indoor tanks: These fish reach 30–45 cm. They are pond fish that happen to be sold in small bags at funfairs. An indoor tank is not appropriate for most adults.
- Koi: Pond fish. Full stop. An adult koi reaches 60–90 cm. There is no indoor tank appropriate for adult koi.
- Tench, bream, roach, or other native fish collected from rivers: Collecting wild fish is regulated by law in the UK and most countries. Additionally, wild-caught fish often carry parasites and pathogens not present in captive-bred stock.
Cycling a coldwater tank — what to expect
The nitrogen cycle in a coldwater tank runs the same biochemical process as in a tropical tank — but beneficial bacteria (Nitrosomonas and Nitrobacter genera) grow more slowly in cooler water. A tropical tank typically cycles in 4–6 weeks. A coldwater tank at 16–18°C may take 6–8 weeks.
Use a fishless cycling approach: add a pure ammonia source (Dr. Tim’s Ammonium Chloride or similar), dose to reach 2–4 ppm ammonia, and wait. Test every 2–3 days. Add a bacterial starter culture (Seachem Stability, API QuickStart, or similar) to accelerate the process. The tank is ready when ammonia and nitrite both read zero within 24 hours of dosing. See our full cycling guide for the complete step-by-step.
The “coldwater is easier than tropical” framing is a sales narrative, not a biological truth. Goldfish are actually more demanding than most tropical community fish in terms of waste production, space requirement, and filtration needs. The only genuine advantage of coldwater is no heater costs and no heater maintenance. The fundamental skills — cycling, water testing, regular changes, appropriate stocking — are identical. If anything, goldfish keeping done properly is more involved than a well-stocked tropical community tank.
Recommended starter setup: 80L planted White Cloud tank
Here’s a specific, proven beginner setup that works beautifully:
- Tank: 80L (e.g. Juwel Rio 80, Fluval Roma 80, or similar)
- Filter: Internal or external canister rated for 100–150L (slightly oversized — always better)
- Substrate: Fine dark gravel or sand, 3–4 cm depth
- Plants: Java fern (on driftwood), anubias (on rock), hornwort or water wisteria as background plants
- Decor: A piece of driftwood, 2–3 smooth river stones
- Fish: A school of 10 White Cloud Mountain Minnows — once the tank is fully cycled
- Optional addition: 3–4 Hillstream Loaches if flow is adequate, or 2 Panda Corydoras (which tolerate slightly cooler temperatures than most corys)
This setup is visually striking, manageable for a beginner, requires no heater, and — with weekly 25% water changes and proper feeding — is one of the most forgiving setups in the hobby. The White Clouds school beautifully in planted tanks and the metallic shimmer of a school moving together is genuinely spectacular.
Plan your coldwater setup, track cycling progress, and monitor parameters with App-aquatic — the free app for every aquarist.
Get the free appWhat temperature should a coldwater fish tank be?
The definition of "coldwater" for aquarium fish is approximately 14–22°C — cool to room temperature. Most UK homes without central heating on full maintain this range naturally. The specific ideal varies by species: White Cloud Mountain Minnows prefer 14–20°C, goldfish 16–22°C, Weather Loach 10–22°C, Hillstream Loach 16–22°C. Keep a thermometer in the tank and monitor seasonal variation — summer overheating is a real risk in unventilated rooms.
Can I keep White Cloud Mountain Minnows with goldfish?
No. Adult goldfish will eat White Cloud Mountain Minnows — minnows are exactly the right size to be a snack. Even if they coexist temporarily (while the goldfish is small), once the goldfish reaches adult size, the minnows will be eaten. Keep these species in separate tanks.
Is a goldfish bowl acceptable for keeping goldfish?
No. A goldfish bowl has inadequate volume, no filtration, no oxygenation, and no cycling. Goldfish kept in bowls die young from ammonia poisoning and oxygen deprivation. This is not the goldfish being fragile — it is the goldfish being kept in conditions that are objectively too small and unfiltered to support life safely. A bowl is decorative furniture, not a functional aquarium.
How often should I do water changes in a coldwater tank?
25–30% weekly is the standard for most setups. Goldfish tanks may need 30–40% weekly due to their high waste output. White Cloud tanks in a well-planted, lightly stocked setup can sometimes extend to fortnightly with good filtration — but weekly is always the safer default. Test your nitrate to guide frequency: if nitrate climbs above 20 ppm between changes, increase frequency or volume.
Do coldwater tanks need live plants?
Not strictly, but live plants improve water quality (absorbing nitrate and ammonia), provide natural hiding spots, and reduce algae by outcompeting it for nutrients. Cold-water tolerant plants — java fern, anubias, hornwort, vallisneria — grow well at 15–22°C and require no CO₂ injection or specialist fertilisers. For beginners, a few low-maintenance plants make the setup significantly more stable and more attractive without adding meaningful complexity.
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