Aquarium
Lid or cover
Jumping is a leading cause of avoidable death in the hobby, and the species most prone to it — hatchetfish, danios, killifish, rainbowfish, loaches, Siamese algae eaters — are all commonly sold without any mention of it.
Short answer
A cover that stops fish jumping out, reduces evaporation, and keeps dust and objects out of the water. For many species it is not optional.
What it does
- Prevents escape
- Reduces evaporation and heat loss
- Keeps contaminants out
Strengths and where it fits
Strengths
- Prevents an entirely avoidable category of loss
- Reduces evaporation, which stabilises hardness
Good fit for
- Almost every tank
- Essential for jumpers and for labyrinth fish
Limitations and where it is the wrong choice
Limitations
- Restricts surface gas exchange if fully sealed
- Condensation drips onto floating plants and rots them
- Air-breathing species need a warm, humid air layer, so a lid is required rather than optional for them
Poor fit for
- Open-top aquascapes with emergent planting — accepting that jumpers cannot be kept in them