Pygmy Corydoras and Chili Rasboras in a 5-Gallon Tank
Yes, pygmy corydoras and chili rasboras can absolutely share a well-planted 5-gallon tank. Honestly, it’s one of the most recommended nano pairings out there, and once you see why, it makes total sense. Both species stay small, both are easygoing by nature, and they claim different parts of the tank, so competition and stress stay low. Here’s how to actually make this combination work.
Why This Pairing Works So Well
Pygmy corydoras (Corydoras pygmaeus) and chili rasboras (Boraras brigittae) get called the “gold standard” nano pair for a handful of solid reasons:
- Size compatibility: Pygmy corys top out around 1 inch (2.5 cm), and chili rasboras rarely pass 0.75 inches (2 cm). Neither one has the size to bully the other.
- Different swimming zones: Corys hug the substrate and lower water column, sometimes drifting mid-tank in a loose group, while chili rasboras hang out in the middle and upper layers, usually near plants. That vertical split keeps territorial squabbles to a minimum.
- Matching water parameters: Both do best in slightly acidic, soft water (pH 6.0-7.0) at 72-78°F (22-26°C). No compromises needed on either side.
- Shared temperament: Both are shy shoalers. Put them in a group with calm company and they relax, show better color, and act the way they would in the wild.
Is a 5-Gallon Tank Really Enough Space?
It can work, but only if you stock conservatively and stay on top of water quality. Here’s a realistic plan:
- 6 chili rasboras (never fewer; drop below 6 and they turn skittish and pale)
- 4-5 pygmy corydoras (same logic, groups of 5+ forage more confidently)
That puts you at roughly 10-11 fish in 5 gallons, which is right at the edge of what’s reasonable for fish this tiny, and only if filtration is strong and water changes happen regularly. Skip adding anything else, shrimp excluded. The bioload margin here is thin, and there’s no room for error.
Setting Up the Tank Correctly
Filtration and Flow
Go with a gentle sponge filter, or a low-flow hang-on-back with a pre-filter sponge over the intake. Chili rasboras hate strong current, and pygmy corys get rattled if they’re constantly being pushed around mid-forage.
Substrate Matters More Than You Think
Pygmy corys sift through the substrate with their barbels while hunting for food. Fine sand or smooth, rounded gravel is the way to go. Skip anything sharp-edged. Over time it wears down their barbels and opens the door to infection.
Plant It Heavily
Both species come from shaded forest streams, and open water makes them nervous. Dense planting isn’t a nice-to-have here, it’s the baseline:
- Floating plants (frogbit, salvinia) to cut the light and recreate that canopy feel
- Fine-leaved plants like java moss or Cryptocoryne for the rasboras to dart through
- A few open sand patches so the corys have room to forage without obstacles
Lighting and Water Changes
Keep the lighting on the softer side. Both species evolved in dim, tannin-stained water, and strong light tends to wash out their color and stress them. Stick to 20-30% weekly water changes; with 10+ fish crammed into 5 gallons, ammonia and nitrate can spike faster than you’d expect.
Feeding Both Species Together
Since corys eat near the bottom and rasboras feed mid-water, there’s barely any overlap or competition:
- Sinking pellets or wafers for the corys, ideally after lights-out or once the rasboras have already eaten
- Micro pellets or crushed flakes for the chilis at the surface and mid-water
- Occasional live or frozen baby brine shrimp, which sharpens color and gets both species breeding-ready
Common Mistakes to Avoid
- Understocking the shoals: Keep only 2 or 3 of either species and you’ll see chronic hiding, stress, and dull color.
- Skipping the cycle: A 5-gallon tank cycles quickly, but it crashes just as quickly. Cycle it fully before any fish go in.
- Letting temperature drift: Small volumes swing fast. A heater with a real thermostat isn’t optional here.
- Overfeeding: In this little water volume, leftover food fouls things almost instantly.
Final Verdict
Pygmy corydoras and chili rasboras make a proven, reliable pairing for a 5-gallon planted tank, as long as you keep stocking conservative (think 4-5 corys, 6 rasboras), filter gently, and stay consistent with water changes. Their size, temperament, and the way they split up the water column make this one of the safest nano combos you can put together. Just resist the urge to add anything else, and this little ecosystem will do just fine.