Hi Chimchase,
I'm guessing you still want the Arrow to be on screen after the "hit"?
What if you make a Instance variable Boolean on the Arrow object, have it set to "True" from start?
This way the Arrow can only collide and remove HP one time only.
So in the code you write something like:
If collides with Player
If Arrow Variable1 = true
Then
set Variable1 = false;