i housed freshwater clams in a 55 gallon sump that i built for one of my 125 gallon tanks. they are definately beneficial to the system unless of course they die, which is quite easy to do. just like a snail your water has to be pristine to ensure they dont die. i obtained my clams from a local resivior. i do not know how they would fare in a filter sock unless it is completely submerged. goodluck and keep on experimenting, that is the reason we are all obsessed with this hobby. and for the record the benefit they have on the water quality outweighs the downfall their waste has impact on it, that is why they are called filter feeders. they clean the water just as a plant or other filter feeder would.