If you have any little critters, snails or such you might want to have the plastic intake screen that comes with the pumps. Sponge filters if not cleaned regularly might cause excess nutrients to build up in the sponge and cause problems. Even if some how a piece of gravel or rock would get sucked into the pump would possibly take out the impellers. What size of pump is it? I think I have some parts for a 600 and a 1200. You are welcome to the screens if I can find them.
Jeff