Can Allen's Rainbowfish and Flash Pleco (L204) Live Together?

Allen's Rainbowfish is a peaceful species (2/10), while Flash Pleco (L204) is generally mild-mannered (4/10). This modest difference means Flash Pleco (L204) may occasionally assert dominance over Allen's Rainbowfish.

In terms of spatial distribution, Allen's Rainbowfish prefers the Top (Surface) and Middle (Open Water) zones, whereas Flash Pleco (L204) occupies the Bottom (Substrate) zone. Because they use different levels of the water column, territorial disputes are less likely and the tank will appear more balanced.

Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion.

Worth noting: Flash Pleco (L204) is nocturnal and will be most active after lights-out, naturally reducing daytime encounters. Also, Allen's Rainbowfish 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 Allen's Rainbowfish and Flash Pleco (L204) to establish separate territories. Add plenty of line-of-sight breaks using driftwood, rocks, and dense planting to reduce territorial confrontations. A larger aquarium with ample hiding spots can help diffuse aggression and give the less dominant fish space to retreat.

The safe temperature window for both species falls between 24°C and 29°C. Aim for the midpoint of this range (around 26.5°C) for optimal comfort.

Both fish can tolerate a pH between 6 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 4–15 dGH. Regular testing will ensure conditions stay within this range.

To house Allen's Rainbowfish and Flash Pleco (L204) together, plan for an aquarium of at least 150 litres with a minimum length of 120 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 - lighly covered, Driftwood (Digestion/Hiding), Smooth Gravel (Sensitive Barbels). Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Flash Pleco (L204) is a plant destroyer, which conflicts with Allen's Rainbowfish'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.