Can Molly (Sailfin/Black/Dalmatian) and Pygmy Rainbowfish Live Together?

Both Molly (Sailfin/Black/Dalmatian) and Pygmy Rainbowfish are generally mild-mannered species with an aggression score of 3/10. Their matching temperaments mean neither fish is likely to dominate the other in a shared aquarium.

Molly (Sailfin/Black/Dalmatian) and Pygmy 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: Pygmy Rainbowfish is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 24°C and 28°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.

Both fish can tolerate a pH between 7.5 and 7.8. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 12–15 dGH. Regular testing will ensure conditions stay within this range.

To house Molly (Sailfin/Black/Dalmatian) and Pygmy Rainbowfish together, plan for an aquarium of at least 75 litres with a minimum length of 60 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: Plants - Densely covered, Established Algae (Otocinclus), Plants - lighly covered. Meeting these requirements will help both species thrive.

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

This pairing usually fails when the tank is treated like a standard mixed community and the caution flags are ignored. Molly (Sailfin/Black/Dalmatian) and Pygmy 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.