I designed these floating rings to help create holes for light to go through as the surface of my aquarium is covered in floating live plants. This is a good way to see in, let light through and creates a spot to feed the fish. I have made the rings at 20cm, 15cm, 10cm and 6cm. They have holes around the edge that are 1.8mm in diameter so that you can use a scrap piece of filament to glue the rings to each other to create longer chains. Hope this is useful to other enthusiasts!

Update There is also now a version available with no holes to improve water-tightness!