Flo-n-Gro 6-Site Ebb & Flow Expansion Kit The expansion kit is Fully compatible with the 12 site ebb & flow GRO system, as well as the 6 site GRO system The 6 site expansion kit allows you to increase your yield without a huge investment The kit comes with six (6) 4 gallon GRO sites and six (6) 3 gallon 360 Degree snap in mesh aeration inserts