Drygoods And Aquarium Supplies Overflow Boxes

About Overflow Boxes: Overflow boxes let water flow out of your aquarium down into your sump. If you do not have built-in overflow, the alternative is to attach a hang-on overflow. An advantage to overflow boxes is that it skims the surface of the water or provides surface agitation. Without surface agitation, there would be a film of dirty build-up on your water.