well my tank is pretty established so i havent seen any problems so far.
If they get stressed, they will tend to swim at the bottom, and you have to watch for any percussions that will go through to the tank because the HF gets scared very easily.
Mine has bashed their heads on the hood a couple times because my mom always walks on her heels and it makes the tank shake (she is considered underweight yet she scares the bejebus out of my HF)
hope that helped
