some aros jus dont like the change, or the action givin during a water change. it must be stressful havin to swim around while ur water volume is dropping, its gettin stirred up n cloudy from crap in the gravel. then filling back up with water then doesn't match the same params. i'd freak out too... but my fish dont. there all used to it n actually enjoy water changes. get all excited like they kno fresh waters comin lol