Can Betta Smaragdina and Koi Live Together?

Betta Smaragdina is a moderately assertive species (5/10), while Koi is peaceful (2/10). This modest difference means Betta Smaragdina may occasionally assert dominance over Koi.

Betta Smaragdina and Koi 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: Betta Smaragdina is a known jumper, so a tight-fitting lid is essential.

To improve the chances of a peaceful coexistence in this community tank: Provide a significantly larger tank (at least 50% more volume than the minimum) to allow both Betta Smaragdina and Koi to establish separate territories. Add plenty of line-of-sight breaks using driftwood, rocks, and dense planting to reduce territorial confrontations.

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.

Both fish can tolerate a pH between 6.5 and 7.5. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 4–12 dGH. Regular testing will ensure conditions stay within this range.

To house Betta Smaragdina and Koi together, plan for an aquarium of at least 3785 litres with a minimum length of 300 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, Plants - Floating, Leaf Litter/Blackwater, Sand (Sifters), Smooth Gravel (Sensitive Barbels). Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Koi is a plant destroyer, which conflicts with Betta Smaragdina's requirement for live plants. Compromise where possible or prioritise the more critical need.

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