Mother Earth Coco Covers are a naturally derived replacement for plastic covers. These 100% natural coconut coir fiber covers work great for preventing algae from growing on top of your rockwool blocks. Available in 4 and 6 inch squares for use with Grodan blocks. Also available is the 8 inch custom cover with rounded corners for use with the Flo-n-Gro Ebb & Flow systems and the Drip-n-Gro system. Tired of algae growing on top of your media, Mother Earth has you covered.