This is the cheat sheet I wish I had when I started keeping nano tanks. Fifteen specific stocking combinations, each one tested either in my own fishroom or by keepers I trust, each one with the bioload percentage, the compatibility logic, and the special requirements called out explicitly. Print this page, take it to the fish store, and use it as a reality check on whatever the employee is trying to sell you. The combinations are ordered roughly by tank size — 5 gallon first, 40 gallon last — so you can scan to the section that matches your tank and pick from the options that fit.
Each combo card has four pieces of information: tank size and fish list (in bold), bioload percentage (the share of the tank's rated capacity the combo occupies — anything under 80% is comfortable, 80–95% needs careful maintenance, over 95% is asking for trouble), compatibility notes (why these fish work together), and special requirements (water parameters, hardscape, plant cover). Verify bioload yourself with the stocking calculator or the nano stocking wizard before you buy fish — the numbers here are my best estimates and your specific fish count may differ. If a combo needs soft acidic water and your tap is liquid rock, pick a different combo — do not try to fight your water.
How to Read the Combos
The bioload percentages in this guide are calculated against the rated capacity of each tank using the standard adult-size formula in our stocking calculator. Nano fish are weighted less than the "1 inch per gallon" rule of thumb would suggest because they produce disproportionately less waste per centimetre of body length than larger fish — a 2 cm chili rasbora does not produce the same bioload as 2 cm of goldfish. The numbers below reflect that weighting. If your tank is heavily planted, you can push toward the upper end of the percentage range; if it is unplanted, stay 10–15 percentage points below the listed number.
Compatibility in nano tanks comes down to three things: water chemistry (all fish must thrive in the same pH, GH, and temperature range), vertical stratification (mid-water fish should not compete with bottom-dwellers for the same space), and behavioural matching (no aggressive species with shy species, no fin-nippers with long-finned species, no predators with prey species you want to keep alive). Every combo in this list passes all three tests. If you modify a combo by swapping a species, re-check all three before you commit.
The special requirements line is the one most keepers ignore and then regret. A combo that needs soft acidic water will not thrive in alkaline tap water no matter how carefully you acclimate. A combo that needs a sand substrate will not work with gravel. A combo that needs dense plant cover will crash without it. Read the special requirements line twice before you start buying fish — it is the difference between a tank that runs for years and a tank that crashes in three months.
5 Gallon Combos
Combo 13: The Betta & Shrimp 5 Gallon
5 gal — 1 Betta + 5 Cherry Shrimp (shrimp may get eaten)
Bioload: ~35%. Compatibility: risky. A single male betta in a heavily planted 5 gallon with 5–10 cherry shrimp is the smallest "real fish" tank in the hobby. The betta claims the whole tank; the shrimp work the surfaces. The catch: some bettas ignore shrimp entirely, others hunt them to extinction in a week, and you find out which kind you have when your colony disappears overnight. Special requirements: dense plant cover (Java moss, subwassertang, floating plants) for shrimp refuge, no fin-nipping tank mates (none in this combo, but worth noting), 25% weekly water changes because the 5 gallon volume is unforgiving. Cycle the tank fully before adding either species — a 5 gallon crash kills both. See the cherry shrimp care sheet for shrimp-specific parameters.
Combo 14: The Shrimp-Only 5 Gallon
5 gal — 20+ Cherry Shrimp (colony)
Bioload: ~10%. Compatibility: perfect (single species). The shrimp-only 5 gallon is the most rewarding small tank in the hobby — a colony of 20 starter shrimp will be 100 within a year, the bioload is trivial, and the lifecycle (berried females, baby shrimp hiding in moss, juveniles colouring up) plays out in front of you on a three-week loop. Special requirements: pH 6.8–8.0, GH 8–15 dGH (crucial for molting — add crushed coral if your tap is soft), temperature 20–26°C, a sponge filter (never an HOB — it sucks up babies), and dense moss cover for baby refuge. No fish, ever. Use the cherry shrimp care sheet and the nano shrimp hub for full parameters.
10 Gallon Combos
Combo 1: The Classic 10 Gallon Community
10 gal — 12 Chili Rasbora + 6 Pygmy Cory + 10 Cherry Shrimp
Bioload: ~55%. Compatibility: excellent. The benchmark 10 gallon nano community. Chili rasboras (Boraras brigittae) school mid-water, pygmy corydoras work the substrate, cherry shrimp clean the surfaces — every niche filled, no competition between species. Special requirements: pH 6.0–7.0 (chili rasboras want soft, acidic water; cherry shrimp will tolerate it), temperature 24–27°C, sand substrate for the corys, dense plant cover (the chilis school tighter with cover). The shrimp colony will breed but losses to the rasboras are possible — accept it as a feature, not a bug. See the chili rasbora and pygmy corydoras care sheets.
Combo 2: The Betta & Pygmy Cory 10 Gallon
10 gal — 1 Betta + 6 Pygmy Cory + 2 Nerite Snail
Bioload: ~45%. Compatibility: good with a male betta, risky with a female sorority. A single male betta in a 10 gallon with a school of 6 pygmy corydoras and 2 nerite snails is a classic low-stress community. Pygmy corys school mid-water (unlike larger cory species that stay on the bottom) and their speed and school size keeps them off the betta's radar. Nerite snails handle algae without competing. Special requirements: pH 6.5–7.5, temperature 25–27°C, sand substrate, no bright-coloured long-finned fish (the betta may attack them), plenty of cover to break the betta's line of sight. Avoid female betta sororities in a 10 gallon — they need a 20 gallon minimum to manage hierarchy stress.
Combo 3: The Pea Puffer & Sacrificial Shrimp 10 Gallon
10 gal — 1 Pea Puffer + 10 Cherry Shrimp (sacrificial colony)
Bioload: ~30%. Compatibility: predatory. Pea puffers (Carinotetraodon travancoricus) are micro-predators that need snails in their diet to wear down their beak — and they will absolutely hunt cherry shrimp if given the chance. The strategy is to keep a self-sustaining cherry shrimp colony as the puffer's food source: the shrimp breed fast enough to outpace the puffer's appetite, and the puffer gets enrichment and a natural diet. Special requirements: pH 6.5–7.5, temperature 24–28°C, dense plant cover for shrimp refuge, a separate snail breeding tank (pond snails or ramshorns) for beak-wearing, and the temperament to accept that the shrimp colony exists primarily as food. See the pea puffer care sheet.
Combo 4: The Shell Dweller 10 Gallon
10 gal — 6 Shell Dweller (Neolamprologus multifasciatus) + 15–20 escargot shells
Bioload: ~35%. Compatibility: single-species (no tank mates). The shell dweller 10 gallon is the most behaviour-rich small tank in the hobby. N. multifasciatus are the smallest cichlid in the hobby at 4 cm, and a colony of 6 will claim individual shells, dig the sand around them, and breed constantly — you will have fry within three months. Special requirements: hard, alkaline water (pH 7.8–8.5, GH 10–15 dGH — Tanganyika parameters), fine sand substrate 3–5 cm deep for digging, escargot shells (one per adult + spares), no other fish (the 10 gallon is the colony's territory and adding anything else is asking for trouble). See the shell dweller care sheet.
15 Gallon Combos
Combo 15: The Endler's & Pygmy Cory 15 Gallon
15 gal — 8 Endler's Livebearer + 6 Pygmy Cory + 3 Amano Shrimp
Bioload: ~50%. Compatibility: excellent. Endler's livebearers (Poecilia wingei) are the energetic surface dwellers of this combo — small (3–4 cm), bright, and constantly in motion at the top of the water column. Pygmy corydoras occupy the mid-water and substrate, Amano shrimp handle algae and clean up leftover food. Special requirements: pH 7.0–8.0, GH 8–20 dGH (Endler's want harder water — they are livebearers), temperature 24–28°C, sand substrate for the corys, some surface cover (floating plants or tall stem plants) for the Endler's to feel secure. Plan for the Endler's to breed — a single male-female pair will produce fry every 4 weeks — and either sex-separate the population or accept steady population growth. See the pygmy corydoras and Amano shrimp care sheets.
20 Gallon Combos
Combo 5: The Apistogramma Harem 20 Gallon
20 gal — 1M + 2F Apistogramma + 10 Ember Tetra + 6 Pygmy Cory
Bioload: ~60%. Compatibility: excellent with harem structure. The 20 gallon long is the minimum footprint for an Apistogramma harem — the male patrols the whole tank, each female claims a 15 cm territory around her cave. Ember tetras are mid-water dithers that make the Apistogramma feel safe; pygmy corydoras work the sand without competing for territory. Special requirements: soft, acidic water (pH 5.5–6.8, GH 2–8 dGH — Apistogramma will not thrive in hard water), temperature 24–26°C, sand substrate (Apistogramma sift sand through their gills — gravel damages them), three cave options (one per female plus a spare), driftwood to break sight lines between female territories. See the Apistogramma care sheet and nano cichlid hub.
Combo 6: The German Blue Ram & Ember 20 Gallon
20 gal — 1M + 1F German Blue Ram + 12 Ember Tetra + 3 Otocinclus
Bioload: ~55%. Compatibility: good with a bonded pair. A focused ram tank — the pair claims half the tank each, ember tetras occupy the mid-water as dithers, and Otocinclus work the algae on hard surfaces. Visually one of the most striking 20 gallon tanks you can build. Special requirements: warm, soft water (pH 6.0–7.0, GH 3–8 dGH, temperature 27–29°C — GBRs are temperature-sensitive and stress below 27°C), sand substrate (rams sift sand — gravel damages gills), and a fully cycled tank before adding rams (trace ammonia kills them in 48 hours). The ember tetras and Otocinclus tolerate the higher temperature. See the German blue ram and ember tetra care sheets.
Combo 7: The Kribensis & Neon Tetra 20 Gallon
20 gal — 1M + 1F Kribensis + 10 Neon Tetra + 1 Bristlenose Pleco
Bioload: ~70%. Compatibility: good with a bonded pair. Kribensis (Pelvicachromis pulcher) are the most adaptable dwarf cichlid — they thrive at neutral pH, which lets you keep them with neon tetras (which want similar water). The bristlenose pleco handles algae; the neon tetras are mid-water dithers. Special requirements: pH 6.5–7.5 (kribensis are adaptable, neons want slightly acidic), temperature 25–27°C, sand substrate (kribensis dig), driftwood for the bristlenose to graze, and a cave for the kribensis pair to spawn in — they WILL breed, and the pair will defend the spawn aggressively. See the kribensis, neon tetra, and bristlenose pleco care sheets.
Combo 8: The CPD & Pygmy Cory 20 Gallon
20 gal — 12 Celestial Pearl Danio + 6 Pygmy Cory + 15 Cherry Shrimp
Bioload: ~45%. Compatibility: excellent. The CPD 20 gallon is the nano community for keepers who want colour without cichlids. Celestial pearl danios (Danio margaritifer) school mid-water and display their galaxy-spotted pattern under good light; pygmy corydoras work the substrate; cherry shrimp breed in the cover. Special requirements: pH 6.5–7.5, GH 5–12 dGH, temperature 22–26°C (CPDs prefer cooler water — do not push above 26°C), sand substrate, dense plant cover (CPDs are shy without cover and school tighter with it). The shrimp colony will breed successfully in this combo — CPDs have small mouths and the moss cover gives babies refuge. See the celestial pearl danio care sheet.
Combo 9: The Scarlet Badis 20 Gallon
20 gal — 1M + 2F Scarlet Badis + 10 Chili Rasbora + 10 Cherry Shrimp
Bioload: ~40%. Compatibility: good with careful sex ratio. Scarlet badis (Dario dario) are tiny (1.5–2 cm), shy, and the males are intensely territorial with conspecifics — one male with two females in a 20 gallon planted tank works; two males will fight to the death. Chili rasboras are mid-water dithers that help the badis feel secure; cherry shrimp work the surfaces. Special requirements: pH 6.5–7.5, GH 4–10 dGH, temperature 22–26°C, dense plant cover (the badis are micro-predators that hunt from cover — without it they starve), live or frozen food only (badis rarely accept flake), and patience — you will not see the badis for the first week. See the scarlet badis care sheet.
40 Gallon Combos
Combo 10: The Apistogramma Harem 40 Gallon
40 gal — 1M + 3F Apistogramma + 15 Cardinal Tetra + 6 Sterbai Cory
Bioload: ~65%. Compatibility: excellent with harem structure. The 40 gallon breeder gives you room to scale up the Apistogramma harem — 3 females instead of 2, with each claiming a 20 cm territory. Cardinal tetras are the larger, more colourful cousins of neons and school tightly in a 40; sterbai corydoras are the warm-water cory species (they tolerate the 27°C the Apistogramma prefer) and they are larger and more visible than pygmy corys. Special requirements: soft, acidic water (pH 5.5–6.8, GH 2–8 dGH), temperature 25–27°C (sterbai are warm-water corys — this is the only cory species that works with Apistogramma temperature-wise), sand substrate, four cave options (one per female + a spare), driftwood to break sight lines. See the Apistogramma care sheet and the nano cichlid hub.
Combo 11: The Tanganyika 40 Gallon
40 gal — 10 Shell Dweller (multifasciatus) + 2 Neolamprologus leleupi
Bioload: ~45%. Compatibility: excellent with niche separation. A proper Tanganyika community in a 40 breeder — the shell dwellers work the sand and shells, the leleupi (a small rock-dwelling Lamprologus) claim a rock pile at one end. Different niches, same water, no competition. Special requirements: hard, alkaline water (pH 7.8–8.5, GH 10–15 dKH — non-negotiable, Tanganyika fish will not thrive in neutral water), temperature 24–27°C, fine sand substrate 4–5 cm deep for digging, escargot shells (20+), a rock pile with caves for the leleupi. If your tap is soft, this combo is not for you — do not try to buffer your way there. See the shell dweller care sheet and search the fish database for Tanganyika species.
Combo 12: The Mixed Dwarf Cichlid 40 Gallon (Heavily Planted)
40 gal — 1M + 1F Ram + 1M + 1F Apistogramma + 15 Ember Tetra + 8 Pygmy Cory
Bioload: ~75%. Compatibility: good with broken sight lines — heavily planted. The 40 breeder lets you mix two dwarf cichlid species if you commit to breaking sight lines and providing enough territory. The ram pair claims one end, the Apistogramma pair claims the other, the ember tetras school in the middle, and the pygmy corydoras work the sand throughout. Special requirements: soft, acidic water (pH 6.0–6.8, GH 3–8 dGH), temperature 26–28°C (warm enough for the rams, not too warm for the Apistogramma), sand substrate, a piece of driftwood down the middle as a sight-line break, dense planting to break sight lines further, four cave options (two per pair). Run a canister filter rated for 55 gallons and do 40% weekly water changes — this is a higher-bioload combo. See the ram and Apistogramma care sheets.
Tools and Related Guides
Use the stocking calculator to verify bioload for any of these combos with your specific fish count, and the nano stocking wizard for a step-by-step plan tailored to your tank. For related guides and the species care sheets referenced above, start here:
- Best Fish for a 10 Gallon Tank — the species-by-species breakdown behind Combo 1–4
- 10 Gallon Community Tank Guide — setup, cycling, and maintenance for 10 gallon tanks
- Nano Cichlid Hub — the full reference for Combos 4, 5, 7, 10, 11, 12
- Nano Shrimp Hub — shrimp-only setups and shrimp compatibility with fish
- Stocking Calculator — check bioload for any combination
- Nano Stocking Wizard — step-by-step nano tank planning
Frequently Asked Questions
How do I know if a nano fish stocking combination will work?
Check three things: bioload (use the stocking calculator to verify you are under 80% of tank capacity), water chemistry compatibility (all fish in the combo must thrive in the same pH, GH, and temperature range), and behavioural compatibility (no aggressive species with shy species, no fin-nippers with long-finned species, no shrimp-eaters with shrimp you want to keep alive). If all three check out, the combo will work. If any one fails, pick a different combo.
Can I mix cherry shrimp with nano fish?
Yes, with the right fish. Otocinclus, pygmy corydoras, and micro rasboras (chili, brigittae) are safe around shrimp colonies. Anything with a mouth big enough to fit a baby shrimp will eat baby shrimp — including tetras, guppies, and bettas. Provide dense moss cover and accept some losses if you mix shrimp with fish. A self-sustaining colony needs a shrimp-only tank.
What is the smallest tank that can hold a community of nano fish?
A 10 gallon is the realistic minimum for a multi-species nano community. A 5 gallon can hold a single betta or a shrimp-only colony, but it does not have the volume or the footprint for a community of three species. The 10 gallon footprint gives enough room for a mid-water school, a bottom-dweller group, and a clean-up crew without crowding.
How many chili rasboras should I keep together?
Minimum 8, ideally 12 or more. Chili rasboras (Boraras brigittae) are schooling fish that stress and fade in colour when kept in groups smaller than 8. In a 10 gallon, 10–12 is the sweet spot; in a 20 gallon, push to 15–20 for the tightest schooling behaviour and the most natural display.
Which nano fish combo is best for a beginner?
Combo 1 (10 gallon with chili rasboras, pygmy corys, and cherry shrimp) or Combo 15 (15 gallon with Endler's livebearers, pygmy corys, and Amano shrimp) are the most forgiving for beginners. Both are low-aggression, low-bioload, and use species that tolerate a wide water parameter range. Avoid the shell dweller and Apistogramma combos until you have kept a community tank successfully for at least a year.