Breeding tank: how to set up a dedicated spawning aquarium

Breeding fish in a community tank is a lottery: 90 % of fry get eaten by tankmates or parents before you even notice them. A dedicated breeding tank changes the rules — controlled environment, no predators, targeted water parameters.

Why a separate tank

• Eggs and fry are safe from adult fish. • You can lower pH/hardness specifically for spawning without harming the main stock. • Easy to observe and feed fry with 'live dust'. • Easy to medicate prophylactically (methylene blue against egg fungus).

Size and shape

20–40 L is enough for most small species (tetras, rasboras, guppies, betta). Cichlids need 60 L+. A low, wide footprint beats a tall narrow one — more bottom area for spawning substrate.

Minimum equipment

Filter

Sponge filter on an air pump only. Internal and canister filters suck up fry and eggs. Pre-cycle the sponge in your main tank for 2–4 weeks so it's already colonised with bacteria.

Heater

25 W with an accurate thermostat. Temperature swings kill eggs faster than any predator. A backup thermometer is mandatory.

Lighting

Dim or none at all. Most species' eggs are light-sensitive; first-week fry are too. If you need light, keep it weak and ambient.

Substrate and decor

Bare bottom is easiest — fast to clean, uneaten food is visible. Alternative — a thin layer of fine sand. For spawning sites: Java moss, spawning mops (acrylic/wool yarn), a flat stone for cichlids, almond leaves for tetras.

Water parameters

Most tropical species spawn in soft, acidic water: pH 5.5–6.5, gH 2–6, kH 0–3. Achieved with an RO + tap mix plus peat extract or alder cones. Livebearers and cichlids — parameters per species.

Conditioning the breeders

For 2–3 weeks before spawning — keep males and females in separate tanks and feed heavily with live food (bloodworm, artemia, daphnia). This triggers egg development in females.

The spawning trigger

Most common — a 30–50 % water change with slightly cooler (–2 °C) and softer water (mimicking rainfall in nature) plus heavy live feeding. Many species spawn the very next morning.

After spawning

Two scenarios: • Egg-eaters (tetras, barbs) — remove parents immediately after spawning. • Caregivers (cichlids, gouramis) — leave them; they defend the eggs and fry. If eggs are clear with visible eye dots — fertilised; cloudy white — not, remove to prevent fungus.

Fry care

First 3–5 days — yolk-sac stage, they feed on it. Then: infusoria (cultured in a jar with a lettuce leaf), microworms, baby brine shrimp (hatch from cysts yourself). Feed 4–6× per day in micro-portions.

Water changes — 10 % every 2–3 days with a thin siphon (cocktail straw). Abrupt shifts kill fry.

What to avoid

• Internal filters — they swallow fry and eggs. • A freshly cycled tank — ammonia kills fry within 24 hours. • Overfeeding — leftovers rot and breed fungus on the eggs. • Bright lighting — stresses parents and kills eggs.

A breeding tank isn't a 'smaller aquarium' — it's a precision tool. The simpler and more stable, the higher the fry yield.