Can Balloon Molly and Cairns Rainbowfish Live Together?

Balloon Molly is a generally mild-mannered species (3/10), while Cairns Rainbowfish is peaceful (2/10). This modest difference means Balloon Molly may occasionally assert dominance over Cairns Rainbowfish.

Balloon Molly and Cairns Rainbowfish both frequent the Top (Surface) and 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.

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 7 and 7.6. Maintaining a stable value within this band is more important than hitting an exact number.

Hardness requirements are incompatible: Balloon Molly needs 12–25 dGH while Cairns Rainbowfish requires 2–10 dGH.

To house Balloon Molly and Cairns Rainbowfish together, plan for an aquarium of at least 110 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.

Providing a mix of open swimming space and sheltered areas with rocks, driftwood, or plants will keep both species comfortable and allow natural behaviour.

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

Balloon Molly 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.

Balloon Molly and Cairns Rainbowfish are the kind of pair that can look acceptable in a shop but become a maintenance problem at home. The main risk is not a single number in the chart; it is the way incompatible behavior, water needs, or pressure on space compounds over time once both fish are established in the same tank.