What should I put in my Bubble-eyed goldfishes tank that won't make his air sacs pop ?

extend the piping to the bottom of the tank to stop the fish from sticking its face in it. That's what we had to do as the fish store I worked at a long time ago.What should I put in my Bubble-eyed goldfishes tank that won't make his air sacs pop ?
PiranhaWhat should I put in my Bubble-eyed goldfishes tank that won't make his air sacs pop ?
Nothing with sharp edges and only use real or silk plants.