The Blue Malawi 1000 filter system, for fresh and saltwater aquaria up to 400 gal. It consists of the following components: Twin filter towers including the patented drawer and biofilter filled with BactoBalls, and the Ocean Runner OR 3500 circulation pump. This filter is the perfect unit for heavy loaded freshwater aquariums, for example cichlids. However, it can be used for saltwater as well, if combined with an external protein skimmer. Pipe connections to the aquarium: 25mm flow, 40mm return. All components are inside the filter sump on the basic model.