Mechanical filtration - A felt filter sock that captures all water exiting the overflows is very beneficial in capturing any uneaten food but it must be replaced with a clean one on a weekly basis or you end up doing more harm than good since the captured matter will begin to decompose releasing dissolved organics into the water. More frequent changes are even more ideal to prevent this from happening. In a sump-less system employing an external power filter with some felt-like material will achieve similar results.