Possible signs of stress:
rapid swimming along the edges of the tank
gills pointed forward
gills shrinking
hyperactivity, or total inactivity
changes in color
loss of interest in food
floating for long periods
Maybe other people have some to add to this.
Please note: Excess water flow and ammonia are preventable (or testable). It is far better to prevent any of these things from happening, than to wait and look for symptoms of stress. Once the symptoms occur, the animal's life may already be at risk.