One of the best systems on the market. The 55 gal res will support 48 buckets which will require 8 bags of hydroton to fill. It comes with 12 buckets and expansion kits are 6 bucket kits. The system is run by a controller and floods buckets then puts solution back in res. Nice for Ph stablity since the res is so large. You can really grow some plants in this baby. I have 4.