Guide
Good setups for a 300 litre tank
300 litres (~80 US gallons) is a serious footprint - room for impressive communities, multiple centrepieces, or a full cichlid setup. Use our stocking calculator to plan.
- 300 litres (roughly 80 US gallons) opens up three genuinely different paths: a large community with multiple schools, a centrepiece-focused setup built around angelfish or discus, or a dedicated cichlid tank - African or South American.
- Water chemistry decides everything: soft, acidic water (pH 6.0-7.0) for South American fish; hard, alkaline water (pH 7.8-8.5) for Rift Lake cichlids. Don't try to split the difference.
- Filter capacity matters more than tank size: run a canister rated for at least 1,200-1,500 litres per hour, or pair two medium canisters.
- Cycle the tank fully before any fish go in - 4-6 weeks minimum. A 300-litre tank can carry a large bioload but it will still crash if it isn't cycled.
- Stock in stages: add the smallest, least demanding fish first and wait two to three weeks between additions.
- Overstocking is still possible at this size - use a stocking calculator before you buy anything.
Why 300 litres is a genuinely good tank size
Most fishkeeping mistakes happen in tanks that are too small to forgive errors. At 300 litres you get enough water volume that a parameter spike won't wipe out everything overnight, enough footprint to give territorial fish real space, and enough height (most 300-litre tanks run 50-60 cm tall) to actually aquascape properly. It's also the point where keeping discus, angels, or a colony of cichlids becomes realistic rather than a compromise.
The trade-off is real though: filtration, lighting, CO2 if you go planted, and livestock all cost more. Weekly water changes mean moving 60-90 litres at a time. This isn't a size for someone who wants a low-maintenance tank in the corner - it rewards the people who actually enjoy the hobby.
Shops will happily sell you a 300-litre tank and stock it with a random mix of "community fish." The result is usually a chaotic, overstocked mess where nothing thrives. The best 300-litre setups are built around one clear concept - not everything that looks nice at the shop.
Setup 1: The large community tank
A well-planned community is the most versatile use of this size. Done properly, it's genuinely impressive - layered schools at different depths, active cleanup crew on the substrate, and one or two centrepiece species pulling the eye in.
A solid starting framework
Aim for three or four distinct schooling layers, a substrate crew, and a centrepiece pair. Here's a concrete example that works in soft to moderately hard water (pH 6.5-7.4, 5-15 dGH):
- Upper-mid layer: 20-25 Paracheirodon innesi (neon tetras) or Hyphessobrycon amandae (ember tetras) for a tight schooling display.
- Mid layer: 15-20 Trigonostigma heteromorpha (harlequin rasboras) or Puntius titteya (cherry barbs).
- Lower mid: 10-15 Melanotaenia boesemani (Boesemani rainbowfish) - these are active, larger fish that fill space beautifully but need 200+ litres to justify a school.
- Substrate: 12-15 Corydoras - mix two species if you like, e.g., C. sterbai and C. paleatus, keeping 6+ of each.
- Centrepiece: A pair of Trichogaster leeri (pearl gouramis) or, if your hardness allows, a pair of Pterophyllum scalare (angelfish).
- Algae control: One Ancistrus species (bristlenose pleco) - do not put a common pleco (Hypostomus plecostomus) in a 300-litre tank. It will outgrow it.
Buying one or two of each species because "they all said they were community fish." Schooling fish kept in groups of fewer than six are stressed, dull-coloured, and often aggressive. In a 300-litre tank you have no excuse - school everything properly.
Filtration and flow for a community
A single canister rated for 1,200-1,500 l/h gives good turnover without battering small fish. If you're running a heavily planted tank with a high stocking level, two medium canisters give you redundancy - one failure won't kill your fish before you notice. Gentle flow suits most South American and Southeast Asian community species; rainbowfish tolerate stronger current.
Water parameters for community fish
The fish listed above overlap in a sweet spot of pH 6.8-7.4, temperature 24-26°C (75-79°F), and moderate hardness (5-15 dGH). You don't need RO water for this setup - most dechlorinated tap water in the UK and much of Europe lands in this range naturally. Check your local supply before buying anything.
Setup 2: The centrepiece tank
Some fishkeepers want the community to serve as a backdrop for one exceptional species. 300 litres handles that well - it's large enough to keep centrepiece fish in proper numbers without crowding them.
Angelfish as the focus
Pterophyllum scalare genuinely need this much space when kept as a group. Four to six angels in a tall 300-litre tank (60 cm height or more) behave as a natural social unit - you'll see hierarchy, pairing, and eventual breeding behaviour. Back them with 30-40 cardinal tetras (Paracheirodon axelrodi), 12-15 Corydoras sterbai (which share the angels' preferred temperature of 26-28°C / 79-82°F), and a bristlenose pleco. Keep the hardness soft (3-8 dGH, pH 6.5-7.0) and the water warm. Most people keep angels too cool.
Discus - doable, but demanding
A discus community is the most demanding freshwater setup at this size. Six Symphysodon sp. need: temperature 28-30°C (82-86°F), pH 6.0-6.8, very soft water (ideally under 6 dGH), immaculate water quality, and frequent feeding (three to four times daily for juveniles). The filtration needs to handle high feeding rates without accumulating nitrate - many discus keepers do 30-40% water changes twice a week rather than once. Cardinal tetras as dithers work well; most corydoras tolerate the heat, though C. sterbai is the best-suited species.
Discus are not forgiving of inconsistent care. If your schedule means you might miss water changes for a week, don't start a discus tank. The fish are expensive, and the margin for error is small. Start with angels instead - they're a more honest indicator of whether you're ready.
Setup 3: African cichlid tank
300 litres is the minimum sensible size for a proper Malawi mbuna colony, and it's a comfortable size for a Tanganyika community or a mixed Victorian setup. The defining rule: commit to the chemistry. Rift Lake fish need pH 7.8-8.5, hardness 10-20 dGH, and temperature 24-27°C (75-81°F). Everything else follows from that.
Malawi mbuna
The mbuna approach is counterintuitive: you stock heavily to spread aggression. In a 300-litre tank with heavy rockwork, aim for 25-35 fish across 6-10 species. Choose species from compatible aggression tiers - Labidochromis caeruleus (electric yellow) as a calmer anchor species, then add Pseudotropheus acei, Melanochromis auratus (carefully - very aggressive), and Cynotilapia afra. Keep a ratio of roughly one male to two or three females per species to prevent any single male from fixating on one female.
For mbuna, build the rockwork before you fill the tank. You need caves, sight breaks, and multiple territories at different heights. Flat open rock on a bare substrate is not a mbuna setup - it's a recipe for one dominant male killing everything else.
Tanganyika options
Lake Tanganyika offers more variety in approach. Three practical options for 300 litres:
- Shell dwellers: A colony of Neolamprologus multifasciatus or N. brevis with a midwater species like Cyprichromis leptosoma above them. Engaging and unusual.
- Tropheus colony: 15-20 Tropheus moorii of a single colour morph. Highly aggressive internally but manageable at high numbers with lots of cover. Feed a low-protein, high-fibre diet - bloat kills Tropheus quickly if you overfeed meaty foods.
- Frontosa: A group of 6-8 Cyphotilapia frontosa can work in 300 litres while young, but adults reach 30-35 cm and genuinely need a 500-litre-plus tank. Only choose this if you're planning an upgrade.
Setup 4: South American cichlids
South American cichlids tend to run larger and more aggressive than their African counterparts, and most need soft, acidic water - the opposite of Rift Lake setups. 300 litres gives you a few solid options.
A pair of Astronotus ocellatus (oscars) with a group of silver dollars (Metynnis argenteus) as dithers is a classic. Oscars grow to 30-35 cm, produce enormous waste, and need serious filtration - run at least 1,500 l/h and plan for 30-40% weekly water changes. Two oscars in 300 litres is workable but not comfortable long-term; if you can step up to 400 litres, do it.
More practical alternatives: a pair of Heros severus (severums) or Heros efasciatus with a supporting cast of larger tetras and a couple of Geophagus species as substrate sifters. Or go smaller with a Geophagus-only setup - a group of 6-8 G. surinamensis or G. altifrons with soft substrate (they'll rearrange it constantly) and dither tetras is genuinely spectacular.
What most cichlid tanks need to keep nitrate under 20 ppm - more if stocked heavily. See our guide on how often to do water changes.
Getting the cycle right before you stock
None of these setups work if the tank isn't cycled. A 300-litre tank with 35 mbuna or 6 discus produces a significant ammonia load - drop that into an uncycled tank and you'll lose fish within days. Run a full fishless cycle using ammonia dosing before any livestock goes in. It takes 4-6 weeks. There are no shortcuts that reliably work. Read the full process in our guide to how to cycle a fish tank.
Once cycled, add fish in stages - smallest and least sensitive first, wait two to three weeks, test the water, then add the next group. This keeps the biological filtration from being overwhelmed. Track your ammonia, nitrite, and nitrate readings over time; App-aquatic makes it straightforward to log water tests and spot trends before they become problems.
Using "instant cycle" bacterial products as a substitute for a proper cycle rather than a supplement to one. They can shorten the process, but adding 30 fish to a two-day-old tank with a bottle of bacteria is not cycling - it's gambling with expensive livestock.
Filtration, hardscape, and planting
At 300 litres, under-filtering is the most common structural mistake. Go for a canister with a flow rate of at least four times the tank volume per hour - so 1,200 l/h minimum, ideally more. Media matters: mechanical foam to catch solids, biological media (ceramic rings or sintered glass) for bacterial colonisation, and a polishing pad at the output. Clean mechanical media every 2-4 weeks; leave biological media alone unless flow drops significantly.
Hardscape and planting aren't just aesthetic. Territorial fish need sight breaks. Corydoras and substrate-sifting cichlids need fine sand, not sharp gravel. Planted tanks buffer water chemistry and export nitrate naturally - worth the investment if you're keeping soft-water South American species. African cichlid tanks can work with either sand or fine gravel; avoid fine-leaved plants that mbuna will shred.
Track your parameters and get care reminders with App-aquatic.
Get the free appHow many fish can I keep in a 300-litre tank?
It depends entirely on the species. 35 small mbuna cichlids is fine; 35 large South American cichlids is not. Species size, bioload, and behaviour all matter more than headcount. Use a proper stocking calculator for your specific combination, and check nitrate levels - if you're struggling to keep nitrate under 20 ppm with regular water changes, you're overstocked regardless of what any rule says.
Can I mix African and South American cichlids in a 300-litre tank?
No - not practically. African Rift Lake cichlids need pH 7.8-8.5 and
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