Can Electric Blue Johannii and Harlequin Rasbora Live Together?

Electric Blue Johannii is a semi-aggressive species (8/10), while Harlequin Rasbora is peaceful (1/10). This notable difference means Electric Blue Johannii may occasionally assert dominance over Harlequin Rasbora.

Large aggression gap (7 points) between Electric Blue Johannii and Harlequin Rasbora increases stress risk for the more peaceful fish.

Electric Blue Johannii and Harlequin Rasbora 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 28°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.

The pH requirements of Electric Blue Johannii (7.8–8.6) and Harlequin Rasbora (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 Electric Blue Johannii and Harlequin Rasbora together, plan for an aquarium of at least 195 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), Established Algae (Otocinclus), Plants - Densely covered, Leaf Litter/Blackwater. Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Electric Blue Johannii is a plant destroyer, which conflicts with Harlequin Rasbora's requirement for live plants. Compromise where possible or prioritise the more critical need.

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

Electric Blue Johannii and Harlequin Rasbora 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.