Hello. I recently posted about using an old washtub for a few small goldfish. I have since swapped out the washtub for this container pond and added a PondMaster fountainhead/filter kit, sans filter. The unit comes with a foam block surrounding the pump, but not a filter. For 4 small goldfish, should I add a filter? I have been doing frequent water changes, and I vacuum debris off the bottom and use a net to catch additional debris. The filter I was thinking of is the TetraPond Submersible Flat Box Filter, but I'm worried it will take up a lot of room in the container. There are also 2 small water lilies in this pond, along with a few rocks for the fish to hide in. Any feedback would be appreciated.