Why are the fish crowding around the filter?

f there crowding around the part that sucks in water, they might be being pulled in. To prevent your fish from getting their fins caught in the sucker, wrap a piece of thin hose or cheesecloth around it.

Also, the fish might be trying to eat bits of food from the sucker. If this is the case, they are hungry and need to be fed. But, some fish just like the feel of the water hitting their back as it comes out of the filter. Hope I helped.