There is green stuff on the top of the Grow Sponges.

If green stuff has developed on the top of your Grow Sponges, do not worry, it is algae. Algae is a type of plant that likes to grow in places where air, water, and light meet. It is non-toxic and will not harm your plants, though some people may find it unsightly.

Sometimes algae will grow because a label has come off a Seed Pod, allowing more light than usual to enter. If you would like to cover your Seed Pod to prevent light from entering and have lost the label, you can cut a suitable replacement out of a small piece of aluminum foil. Cut a circle out of a piece of aluminum foil, cut a hole in the middle (like a donut), and then carefully make a slit from the edge to the center so that you can slip it around the stems of the plants like a collar. This will deprive the algae of light.