Aquarium fish compatibility handbook

"Can a betta go with guppies?" is the single most common pet-shop question. There's no universal answer — it depends on tank size, group composition, hiding places, and individual temperament. This article gives you a framework for the call.

Four compatibility factors

1. Water parameters

The obvious rule: fish must live in overlapping ranges of temperature, pH, and hardness. A discus (28–30 °C, soft acidic) and a molly (24–26 °C, hard alkaline) are incompatible by parameters alone, however peaceful both may be.

2. Temperament and social behavior

Distinguish: peaceful schooling fish (tetras, barbs), peaceful solitary fish (betta), semi-aggressive territorial (cichlids), predators (African cichlids, bichirs).

A simple rule: "small + large = prey." Any fish smaller than the neighbor's mouth is potential food. Even a peaceful angelfish will eat an adult neon.

3. Biotope and swimming zone

Spreading fish across top, middle, and bottom layers uses tank volume more efficiently. Gourami (top) + neons (middle) + cory (bottom) is a classic minimum-conflict biotope.

4. Numbers

Schooling species without a school turn aggressive or withdrawn. Tiger barbs in a group of 8+ are peaceful; in a trio they fin-nip everything in sight.

Dangerous combinations (never keep together)

• Betta + male guppies — guppy tails trigger attacks.

• Tiger barb + any long-finned fish (angelfish, betta, dwarf gourami) — they shred fins.

• Goldfish + tropicals — different temperatures; goldfish will eat smaller fish.

• African cichlids (Tanganyika/Malawi) + any soft-water species — hard alkaline water kills Amazonian fish.

• Shrimp + large cichlids — shrimp = live food.

Safe classic combinations

Amazon community

From 100 L. Neon tetras (12) + rummynose tetras (8) + bronze corys (6) + bristlenose pleco (1). All peaceful, different zones.

Southeast Asia

From 80 L. Harlequin rasboras (10) + dwarf gourami (pair) + white cloud minnows (10) + 3 bristlenose plecos. Labyrinth fish on top, rasboras in the middle.

Malawi biotope (advanced only)

Hard alkaline (pH 7.8–8.6). Mbuna cichlids in a large group, large tank (300+ L). Intraspecific aggression drops thanks to the "crowd effect."

Principles for beginners

1. Water parameters first — you can't change hardness drastically without RO.

2. Then fish by biotope — it works naturally.

3. Schooling fish — minimum 6 individuals of one species.

4. No direct food threats between species (size ratio).

5. In doubt → don't buy. Easier not to acquire than to rehome later.

Compatibility is not a table but a living system. Each aquarium is unique: the same set of fish behaves differently in different tanks.