The grow flow active aqua flow expansion kit includes six growing modules, each consisting of the square 5-gallon pot with 6 screen fittings, 6 inner buckets, and all necessary connectors and tubing. Each pot features a centered drain fitting that minimizes standing water. Each bucket holds approximately 13 liters of clay pebbles or a similar medium. Please note that a control unit and reservoir (sold separately) are required to use this expansion pack. This grows flow active aqua flow expansion kit is part of the most efficient ebb and flow system on the market. You can connect up to 48 on one control unit, depending on the reservoir size. You can also build your own system from the ground up by purchasing all the components individually.