Although this thing slides up and down the waterline, it is unsafe for curious fish. Now it's almost common to catch the Bolt or Molly that managed to jump into the web. I tried moving the suction cup as high up in the tank as possible, but the weak suction didn't take long to slide back down the waterline. Do you have a lid or keep yours closed. Some stuck fish try to jump out and miss the target. Completely out of the tank.