Can Brown Puffer and Cairns Rainbowfish Live Together?

Brown Puffer is a highly aggressive species (9/10), while Cairns Rainbowfish is peaceful (2/10). This notable difference means Brown Puffer may occasionally assert dominance over Cairns Rainbowfish.

Large aggression gap (7 points) between Brown Puffer and Cairns Rainbowfish increases stress risk for the more peaceful fish.

Brown Puffer and Cairns Rainbowfish both frequent the Middle (Open Water) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.

Worth noting: Cairns Rainbowfish is a known jumper, so a tight-fitting lid is essential.

To improve the chances of a peaceful coexistence in this community tank: Provide a significantly larger tank (at least 50% more volume than the minimum) to allow both Brown Puffer and Cairns Rainbowfish to establish separate territories. Add plenty of line-of-sight breaks using driftwood, rocks, and dense planting to reduce territorial confrontations. A larger aquarium with ample hiding spots can help diffuse aggression and give the less dominant fish space to retreat. Keep fin nippers in larger groups to distribute nipping behaviour among conspecifics rather than tank mates.

The safe temperature window for both species falls between 24°C and 26°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.

Both fish can tolerate a pH between 6.5 and 7.5. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 5–10 dGH. Regular testing will ensure conditions stay within this range.

To house Brown Puffer and Cairns Rainbowfish together, plan for an aquarium of at least 114 litres with a minimum length of 90 cm. This recommendation combines the stricter species minimums with a community-load allowance so the pairing has realistic long-term space and filtration headroom.

Because this pairing requires extra vigilance, include plenty of hiding spots — caves, driftwood, and dense plant clusters — so the less dominant fish can retreat when needed.

Specific environmental needs for this combination include: Sand (Sifters), Shells (Breeding/Hiding), Plants - Densely covered, Smooth Gravel (Sensitive Barbels), Driftwood (Digestion/Hiding), Leaf Litter/Blackwater. Meeting these requirements will help both species thrive.

Brown Puffer prefers Low (Still Water) flow while Cairns Rainbowfish needs High (River/Stream) flow. Consider positioning filter outlets and using baffles to create zones of different current intensity within the same tank.

This pairing usually fails when the tank is treated like a standard mixed community and the caution flags are ignored. Brown Puffer and Cairns Rainbowfish need extra room, more cover, and closer observation during the first few weeks so small aggression, feeding, or territory issues do not snowball into a long-term problem.