Can Cairns Rainbowfish and Sailfin Molly Live Together?

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

Cairns Rainbowfish and Sailfin Molly both frequent the Middle (Open Water) and Top (Surface) 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 22°C and 26°C. Aim for the midpoint of this range (around 24.0°C) for optimal comfort.

Both fish can tolerate a pH between 7.5 and 7.6. Maintaining a stable value within this band is more important than hitting an exact number.

Hardness requirements are incompatible: Cairns Rainbowfish needs 2–10 dGH while Sailfin Molly requires 15–30 dGH.

To house Cairns Rainbowfish and Sailfin Molly 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: Smooth Gravel (Sensitive Barbels), Driftwood (Digestion/Hiding), Leaf Litter/Blackwater, Established Algae (Otocinclus), Plants - Densely covered. Meeting these requirements will help both species thrive.

Both species do well with high (river/stream) water movement, so a standard filtration setup rated for the tank volume should suffice.

Cairns Rainbowfish and Sailfin Molly 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.