Where are your lines? All the way to the lip or the bottom of of the molding of the tank?
In a poly tank, it's best to have the water line lowered a bit. I keep mine down at least an inch to an inch and a half.
This gives them space to breach for air without hitting their faces on the lids. If they're chasing prey such as ghost shrimp, the shrimp usually get stuck to the glass gap between the lid and the water line, flicking themselves off later.
HTH
In a poly tank, it's best to have the water line lowered a bit. I keep mine down at least an inch to an inch and a half.
This gives them space to breach for air without hitting their faces on the lids. If they're chasing prey such as ghost shrimp, the shrimp usually get stuck to the glass gap between the lid and the water line, flicking themselves off later.
HTH
