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. These mesh inserts promote lateral root growth and better aeration for the root zone. The snap in feature keeps your plants from floating in the system. The kit includes 3/4 in exclusive Tub Outlet Tee Fitting and tubing to hook up to your system. BPA free.