# Aquarium fish compatibility checker

> Pick two fish to see whether they can share a community tank and why. The checker uses a compatibility matrix built from temperature requirements, temperament, and documented aggression and predation risks.

## Fish database

| Species | Temperature | Temperament | Min tank | Notes |
|---|---|---|---|---|
| Guppy (Poecilia reticulata) | Tropical | Peaceful | 10 gal | Livebearer; colourful males have long fins. |
| Neon tetra (Paracheirodon innesi) | Tropical | Peaceful | 10 gal | Shoaling; keep in groups of six or more. |
| Betta (male) (Betta splendens) | Tropical | Semi-aggressive | 5 gal | Territorial; males fight each other. |
| Fancy goldfish (Carassius auratus) | Coldwater | Peaceful | 20 gal | Coldwater; heavy bioload; social. |
| Angelfish (Pterophyllum scalare) | Tropical | Semi-aggressive | 30 gal | Cichlid; grows large enough to eat small fish. |
| Peppered corydoras (Corydoras paleatus) | Tropical | Peaceful | 20 gal | Bottom-dwelling; keep in groups of five or more. |
| Cherry barb (Puntius titteya) | Tropical | Peaceful | 20 gal | Shoaling; males are most colourful in groups. |
| Zebra danio (Danio rerio) | Tropical | Peaceful | 10 gal | Fast, active surface swimmer; keep in groups. |
| Oscar (Astronotus ocellatus) | Tropical | Aggressive | 75 gal | Large predatory cichlid; solitary. |
| Tiger barb (Puntigrus tetrazona) | Tropical | Semi-aggressive | 20 gal | Fin nipper; aggression drops in large schools of six or more. |
| Southern platy (Xiphophorus maculatus) | Tropical | Peaceful | 10 gal | Livebearer; very easy community fish. |
| Kuhli loach (Pangio kuhlii) | Tropical | Peaceful | 20 gal | Nocturnal bottom dweller; keep in groups; needs soft substrate. |

## How the check works

Each species is described by its temperature class (tropical or coldwater), temperament, and minimum tank size.

The verdict is incompatible when temperature classes do not overlap, or when a documented predation or aggression risk applies. Conditional means it can work in a large, well-planted tank with careful monitoring. Compatible means the pair is a standard community combination.

Tank size still matters: a compatible pair can fail in a tank that is too small. Use the larger species’ minimum tank size as your baseline.

## Frequently asked questions

**Q: Can a betta live with other fish?**

Sometimes. Bettas can coexist with peaceful bottom-dwellers such as corydoras or kuhli loaches in a planted tank, but they may chase colourful or long-finned fish and will fight other male bettas.

**Q: Do goldfish get along with tropical fish?**

No. Goldfish are coldwater fish (roughly 16–22°C) and tropical fish need warmer water (roughly 22–28°C). Keeping them together stresses both.

**Q: What does "conditional" mean?**

The pair can work under the right conditions — usually a large, planted tank, a big enough school of each species, and close monitoring. It is a riskier choice than a compatible pair.

**Q: Why does tank size matter for compatibility?**

Overcrowding causes stress and aggression even in peaceful species. Use the larger of the two species’ minimum tank sizes, and add more space for groups.

**Q: How many fish can I keep in a community tank?**

Stocking depends on filtration, water changes, and adult size. A common starting rule is 1 inch of adult fish per gallon (about 1 cm per 4 L), but it is a rough guide — check each species’ needs.

Use the interactive checker: https://petguidecalc-dev.pages.dev/aquarium/mix-calculator/

_Verdicts are based on temperature class, temperament, and documented aggression and predation risks. Always use the larger species’ minimum tank size as your baseline. PetGuideCalc — https://petguidecalc-dev.pages.dev_