Japanese Takashi Amano has inspired many aquarium owners to keep the 1-5 cm tall cosmopolitan moss, Riccia fluitans, submerged. It has been kept down by tying it to some mesh, but new shoots always grow towards the surface, so it will be necessary to prune it with scissors.
Riccia fluitans thrives best with added CO2 and in good growing conditions small oxygen bubbles form on the leaf tips. As a traditional floating plant offers good protection for young fish.
Mesh size = 45x45mm