Can Regan's Julie and Rosy Finned Tetra Live Together?

Regan's Julie is a semi-aggressive species (7/10), while Rosy Finned Tetra is peaceful (1/10). This notable difference means Regan's Julie may occasionally assert dominance over Rosy Finned Tetra.

Large aggression gap (6 points) between Regan's Julie and Rosy Finned Tetra increases stress risk for the more peaceful fish.

Regan's Julie and Rosy Finned Tetra 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.

The safe temperature window for both species falls between 24°C and 27°C. Aim for the midpoint of this range (around 25.5°C) for optimal comfort.

The pH requirements of Regan's Julie (8–9) and Rosy Finned Tetra (5.5–7.5) do not overlap, making it impossible to satisfy both species simultaneously.

For general hardness, the shared comfort zone is 10–12 dGH. Regular testing will ensure conditions stay within this range.

To house Regan's Julie and Rosy Finned Tetra 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: Sand (Sifters), Plants - Densely covered, Leaf Litter/Blackwater. 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.

Regan's Julie and Rosy Finned Tetra 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.