Under Current 4-Site Expansion Kit for Under Current Double Barrel or Under Current This 4-Site expansion kit from Current Culture allows you to expand your Under Current Double Barrel system by 4-Sites (1 row) or your Under Current 4-sites (2 rows). This kit is great if you want to grow more, but don't want to go and purchase a whole new system. All Current Culture Systems now come with White ABS lids. These new white lids are made of durable ABS plastic, are UV stable, 100% non-translucent and highly reflective. This provides for slightly cooler system operating temperatures and less scale build up. The black lids previously used have been discontinued and are no longer available. New Side-Entry Air Ports All Current Culture Under Current system now include an innovative side-entry for the air diffuser lines utilizing a uni-seal for each module. This allows you to remove the entire module lid without disconnecting the air lines, making root-zone inspection much easier. Replacement Air Diffuser kits are now sold in two options - side entry or top entry. You can easily convert an older UC system with top entry to utilize side entry by purchasing an air diffuser kit and following the included instructions to drill the correct sized hole into your modules.