Can Dwarf Pencilfish and Sailfin Molly Live Together?

Dwarf Pencilfish is a peaceful species (1/10), while Sailfin Molly is generally mild-mannered (3/10). This modest difference means Sailfin Molly may occasionally assert dominance over Dwarf Pencilfish.

Dwarf Pencilfish and Sailfin Molly 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.

Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion. Aggressive eaters may outcompete shy fish for food, leading to malnutrition.

Worth noting: Dwarf Pencilfish is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 22°C and 28°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.

The pH requirements of Dwarf Pencilfish (4–7) and Sailfin Molly (7.5–8.5) do not overlap, making it impossible to satisfy both species simultaneously.

Hardness requirements are incompatible: Dwarf Pencilfish needs 1–10 dGH while Sailfin Molly requires 15–30 dGH.

To house Dwarf Pencilfish and Sailfin Molly together, plan for an aquarium of at least 110 litres with a minimum length of 80 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: Plants - Densely covered, Plants - Floating, Leaf Litter/Blackwater, Established Algae (Otocinclus). Meeting these requirements will help both species thrive.

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

Dwarf Pencilfish 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.

Feeding time deserves special attention with this pairing. Sailfin Molly is an aggressive eater that may prevent Dwarf Pencilfish from getting enough food.

Because Sailfin Molly is a fast, competitive feeder, consider using sinking pellets or feeding at opposite ends of the setup to ensure Dwarf Pencilfish receives an adequate share.