Bulk Reef Supply 4 Stage Reverse Osmosis Systems are perfect for reefers that have space requirements or relatively clean household water. All of our RODI systems use DOW membranes with NSF certified filters. We offer three different levels of systems each providing additional components over the previous. Choose between the Value, Plus, or Plus Water Saver models. We specifically design our RODI systems for use on reef tank and other types of marine aquariums.