Community Tank Planning: Building a Balanced Aquarium
Start with your tap water
Test your tap water for pH and hardness before choosing a single species. If it comes out of the tap at pH 7.8 and 15 dGH, build a hard-water community — livebearers, danios, barbs — and you will never fight your water again. If it is soft and acidic, build a South American tank. Choosing fish first and then modifying water chemistry weekly is the most common route to a frustrating hobby.
Fill the three zones
| Zone | Role | Examples |
|---|---|---|
| Top | Movement and colour near the surface | Zebra Danio, Guppy, Endler's Livebearer |
| Middle | The main shoal — visual centre of the tank | Harlequin Rasbora, Cardinal Tetra, Cherry Barb |
| Bottom | Activity and substrate cleaning | Bronze Corydoras, Kuhli Loach, Bristlenose Pleco |
| Centrepiece | One larger focal fish | Honey Gourami, Pearl Gourami, Bolivian Ram |
Fewer species, bigger groups
This is the single change that most improves an amateur tank. Twelve of one shoaling species looks vastly better than four each of three species, costs the same, and is far healthier for the fish. Shoals only display natural behaviour and full colour once the group is large enough to feel secure.
Worked plans
20 gallon long
10 Harlequin Rasbora (mid) + 6 Pygmy Corydoras (bottom) + 1 Honey Gourami (centrepiece) + nerite snails. Hardy, peaceful, all zones covered.
29 gallon planted
12 Cardinal Tetra + 8 Bronze Corydoras + 1 Pearl Gourami + a colony of Cherry Shrimp in the moss. Soft water only.
55 gallon community
15 Zebra Danio (top) + 12 Harlequin Rasbora (mid) + 8 Bronze Corydoras (bottom) + 1 Bristlenose Pleco. Robust, hard-water tolerant, easy.
Add fish in the right order
Hardiest first, most territorial last. Adding a territorial species first lets it claim the entire tank before anyone else arrives. Leave two weeks between additions so the filter can catch up and so any disease in new stock shows itself before it spreads.
Model the whole plan in the stocking calculator before spending anything.
Frequently asked questions
How many species should a community tank have?
Two to four for most tanks under 40 gallons. Fewer species with larger groups looks better and is healthier than many species in small numbers.
What order should I add fish to a community tank?
Hardiest and least territorial first, most territorial last, with about two weeks between each addition so the filter bacteria can expand and disease can be spotted early.
Can I mix soft water and hard water fish?
It is best avoided. One species will always be living outside its comfortable range, which suppresses the immune system over months rather than causing obvious immediate problems.
What is a centrepiece fish?
A single larger, more visually striking fish that gives the tank a focal point — typically a gourami, ram or similar species in the 2–5 inch range.
Next steps
Written and reviewed by Marcus Rivera. See our methodology for how figures on this site are derived.