The Under Current® XL13 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® XL13 back in working order. Under Current® XL13 Expansion Kit includes: one 13 gallon with a 30 in center blackout series per growth module, 3 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. 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.