This kit includes 4 Hydrofarm GFOE2 Active Aqua 2 Gallon Grow Flow Expansion Kit, 2 Aqua Grow Flow Ebb and Gro Controller Unit, and 2 55 Gallon Drum Hydroponic Reservoirs. The Grow Flow Expansion Kit includes six growing modules, each consisting of a round 2-gallon pot with ½" fittings, an inner bucket, and all necessary connectors and tubing. Each pot features concave bottom with multiple drain holes for better water flow. Active Aqua's Grow Flow is the most efficient ebb & flow system on the market. With the Grow Flow's easy-to-program controller unit, you can pretty much "set it and forget it." And since your pumps are only pumping a short time each day, the system is extremely reliable and efficient. Just set the fill and drain cycles, and the controller unit does the rest! As for safety, the Grow Flow is the only unit available with fail-safe overflow protection. If the float valve stops operating, the LED indicator lights up on the control panel and the emergency shut-off valve automatically shuts down the system, preventing any spillage or damage to your growing area. Have bigger plans? With the convenient included Grow Flow Expansion Kits you can connect up to 24 growing modules to a single 5-gallon system and up to 48 modules with the 2-gallon system! You can also build your own system from the ground up by purchasing all the components individually. This high-quality 55-gallon drum is black in color and comes with a pre-drilled solid cover and bolt ring closure. It is perfect for use as a reservoir for larger hydroponic systems. The pre-drilled holes can be used for the grommets and barbed fittings necessary to outfit the drum with tubing for filling and draining. A larger hole can also be cut in the cover to act as a port for adding nutrients, checking pH, etc. Pair this drum with the included Active Aqua Grow Flow accessories to create the most efficient ebb & flow system on the market.