3" rockwool cube cap - cover  Algae growth on the top surface of your cubes can become a breeding ground for harmful pathogens. Cube Caps offer the ultimate solution to preventing both Algae and fungus gnats without adding any chemicals and without suffocating your roots. Reusable from crop to crop, Cube Caps are available to fit both 7.5cm (3 inch) and 10cm (4 inch) transplanting cubes. Highly recommended if growing in an NFT system.