While doing my weekly 50% water change today one of my Festivums got it's head stuck in the siphon. The fish is about 3-4", the siphon hose is 3/4". I stopped the siphon to get it out. It's head is a bit mangled and it has a bulging eye. This has never happened to me before, I might change to a 1/2" siphon to reduce the suction.