The Under Current® XL Expansion Kits are great for replacing a growth module in a situation where one of the original modules has been damaged or broken in any way. These kits come with all you need to get your Under Current® XL back in working order. Under Current® XL Expansion Kit Includes: one 8 gallon with a 25 in center Blackout Series per growth module, 2 in connecting joints with UC Spin-Tight Bulkhead, growth module lid, one 8 in net pot per growth module, one Aqua-Pore Air Diffuser per module and it does not include any additional air or water pumps which may be required. Choose from 1 site, 2 site, 3 site or 4 site replacements. These items are drop ship only.