20-Gallon Stocking Plans: 4 Balanced Community Tanks
Twenty gallons is where community tanks get interesting: enough water for a real school, a bottom crew, and a centrepiece — as long as the three groups are chosen to share one temperature and leave each other alone. These four plans do exactly that.
Plan 1 — The Complete Community
| Fish | Number | Role |
|---|---|---|
| Neon Tetra | 12 | Mid-water school |
| Pygmy Corydoras | 8 | Bottom (and mid-water) group |
| Honey Gourami | 1 | Centrepiece, top |
Stocking level: 88% — comfortable. Set temperature: 77–78 °F. This is the plan we'd hand a beginner who asked for "a proper community tank." The gourami is peaceful enough not to bother tetras, the pygmy corydoras are small enough to keep in a real group, and every layer of the tank has life in it. Add in stages: tetras first, corydoras a week later, the gourami last so it settles into an established community.
Plan 2 — The Big School
| Fish | Number | Role |
|---|---|---|
| Neon Tetra | 15 | The whole show |
| Cherry Shrimp | 10 | Clean-up colony |
Stocking level: 80% — comfortable. Set temperature: 72–78 °F. Fifteen neons behave completely differently from six: the school tightens, splits and reforms like a single organism. A 20-gallon "long" shows this best. The shrimp add a self-sustaining clean-up crew and a second scale of life to watch. Simple, stable, and the easiest plan here to maintain.
Plan 3 — Colour Up Top, Workers Below
| Fish | Number | Role |
|---|---|---|
| Guppy (all male) | 4 | Colour, top and mid-water |
| Panda Corydoras | 6 | Bottom group |
Stocking level: 90% — comfortable, at the top of the band. Set temperature: 72–77 °F. Guppies bring constant motion and colour; panda corydoras bring the bottom to life without growing large. All-male guppies avoid the fry explosion (mixed sexes in a tank this stocked would overflow it within months). At 90%, treat weekly 25–30% water changes as non-negotiable.
Plan 4 — The Single-Species Showcase
| Fish | Number | Role |
|---|---|---|
| Harlequin Rasbora | 11 | School — and nothing else needed |
Stocking level: 88% — comfortable. Set temperature: 73–82 °F. Harlequins are hardier than neon tetras, slightly larger (2 inches as adults), and school tightly with a distinctive copper-and-black wedge. A single-species tank is the most underrated setup in the hobby: one temperature, one behaviour, zero compatibility risk — and a big group of one fish always looks more natural than a jumble of pairs.
Before you stock any of these
- Cycle the tank first — 2–6 weeks, fishless. The full method: nitrogen cycle guide.
- Stock in stages, one group per week, testing ammonia and nitrite before each addition.
- Adjusting a plan? Check your version in the calculator and keep a first tank at or below 90%.
- Smaller tank? The 10-gallon plans are built for exactly that footprint.