no harm at all ... i use a Python every time i do a water change, which is 50 percent weekly.Could that do harm?
to vaccuum the gravel, obviously a portion of my arm has to be underwater. How much should I was my hand before hand? Does vaccuuming stress the fish?
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my fish never seemed to be stressed when doing gravel vacs. you can use a stick if you dont want to put your hand into the tank if thats what your asking.
As long as you don't purposely chase them around tank, and use slow deliberate movements, it shouldn't put any undue stress on them at all... my fish actually watch the process and "investigate" the areas I've just cleaned! Good luck with your next session.Does vaccuuming stress the fish?