with any filter bag and its small micron size is to filter the tinest debris out of your water however they do clog quickly then you have to clean and lightly bleech what i found work's best for me is to make a pre filter with some PVC pipe and a pvc drain add 50 micron filter pad on top of drain then some filter floss and on top of that a more course filter pad you can then fill your filter sox with bio ball's and add to the denitrification process as well as add to the life of your sox or add carbon to the sox or any of your favorite chemical media replace filter pad's once a month and your chemical media in sox if using bio ball's you never have to replace. I call this method the Lance Lesko filter sox method after the aquarist who founded the idea.