Can Beckford's Pencilfish and Marlier's Julie Live Together?

Beckford's Pencilfish is a peaceful species (2/10), while Marlier's Julie is moderately assertive (6/10). This notable difference means Marlier's Julie may occasionally assert dominance over Beckford's Pencilfish.

Beckford's Pencilfish and Marlier's Julie 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: Beckford's Pencilfish is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 23°C and 27°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.

The pH requirements of Beckford's Pencilfish (5–7.5) and Marlier's Julie (8.2–9.3) do not overlap, making it impossible to satisfy both species simultaneously.

For general hardness, the shared comfort zone is 10–15 dGH. Regular testing will ensure conditions stay within this range.

To house Beckford's Pencilfish and Marlier's Julie together, plan for an aquarium of at least 114 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, Sand (Sifters). 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.

Beckford's Pencilfish and Marlier's Julie 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.