Custom designed "lid" for American Hydroponics 3' x 3' Econo or Heavy Duty trays, Gro-Well is a custom black ABS insert with (36) 1 1/2" wells. It is designed for use with Rockwool cubes. The roots grow through the insert into the tray to form a root mat that is flooded with nutrients. Includes custom overflow fitting to maintain proper water level. This "lid" also creates a cover for the roots of your plants, not allowing any light to penetrate the roots. Achieving the healthiest root zone possible is the key to large, lush plants!