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, 6 and 8 inch squares for use with Grodan blocks. Also the 8 inch custom cover works well with Flo-n-Gro? Ebb & Flow systems. Tired of algae growing on top of your media, Mother Earth? has you covered.