My Chromis love the sump

[blacknife]

One of my local fish stores gave me some kind of filter matt that is about 2 inches thick that i cut to the right size then stuffed over my overflow, have not lost a fish down it since. it is open enough i just need to rinse it out once every week or 2 there is not much in it from my little reef fish. I think its meant more like a pre filter for bigger systems or ponds.