What is your setup like? Normally this is happening for 2 reasons.
1. Your suction is too strong. Solution- you could put more floss in there or you could put an old pair of pantyhose around it and secure it with a rubber band.
2. Your water parameters aren't where they should be and your fish are stressed, weak and are getting sucked up.
Until you give more info on your setup and water parameters, that would be my guess.