So are they darting to the top and dashing down? Or are they glass surfing?
If it is the first, you may have a low oxygen level but that is doubtful considering the other fish are fine. They might just be a bit stressed and I would get them some more conspecifics regardless as this may help lower that stress level.
“Books are my friends, my companions. They make me laugh and cry and find meaning in life.” ― Christopher Paolini, Eragon
"By books you mean fish, right?" ― Raymond