Is it an external?
You can add more media to the filter, filter floss is usually the best for slowing flow down. You could direct the flow towards the glass or place something infront of it, either a rock or some wood etc.
If it is an external with a spray bar then try drilling the holes out a little. Often taking the spray bar off will increase the actual flow from the filter but reduce the intensity as it is not being blasted through a tiny pin hole.
Hope that helps.