Can Royal Pleco (L190) and Threadfin Rainbowfish Live Together?

Royal Pleco (L190) is a moderately assertive species (5/10), while Threadfin Rainbowfish is peaceful (1/10). This notable difference means Royal Pleco (L190) may occasionally assert dominance over Threadfin Rainbowfish.

In terms of spatial distribution, Royal Pleco (L190) prefers the Bottom (Substrate) zone, whereas Threadfin Rainbowfish occupies the Top (Surface) and Middle (Open Water) zones. Because they use different levels of the water column, territorial disputes are less likely and the tank will appear more balanced.

Worth noting: Royal Pleco (L190) is nocturnal and will be most active after lights-out, naturally reducing daytime encounters. Also, Threadfin 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 Royal Pleco (L190) and Threadfin Rainbowfish 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 23°C and 28°C. Aim for the midpoint of this range (around 25.5°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 5–12 dGH. Regular testing will ensure conditions stay within this range.

To house Royal Pleco (L190) and Threadfin Rainbowfish together, plan for an aquarium of at least 450 litres with a minimum length of 150 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: Driftwood (Digestion/Hiding), Plants - Densely covered, Plants - Floating. Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Royal Pleco (L190) is a plant destroyer, which conflicts with Threadfin Rainbowfish's requirement for live plants. Compromise where possible or prioritise the more critical need.

Royal Pleco (L190) prefers High (River/Stream) flow while Threadfin Rainbowfish needs Low (Still Water) flow. Consider positioning filter outlets and using baffles to create zones of different current intensity within the same tank.

This pairing usually fails when the tank is treated like a standard mixed community and the caution flags are ignored. Royal Pleco (L190) and Threadfin Rainbowfish need extra room, more cover, and closer observation during the first few weeks so small aggression, feeding, or territory issues do not snowball into a long-term problem.