The FloraFlex FloraCa 4 inch helps eliminates algae, stops powdery mildew and does away with pesticides. Place on your rockwool cubes, and maximize your space in the vegetative cycle. Each cap features 17 flower designed louvers for the 4 in, to block light, while allowing nutrients water, and air to your plant. Feed your plants less, allow the root zones to dry at more consistent rates with the FloraCap that strategically covers the top of the media, while allowing in the necessary oxygen they need to thrive. Made from BPA and lead-free plastic. Dishwasher safe, stackable and reusable.