The Stars are a porous substrate. They are criss-crossed by a multitude of minute canals precisely designed to let oxygen, water and inert particles circulate freely, so that the environment stays healthy and clean.
You need 7 Stars to give SubCulture the adequate habitat where to thrive.
They are self-cleaning as dead particles in suspension are easily ejected out while the new-born cells replace them naturally. They need no special maintenance. You can rinse them occasionally. It is best to replace them by half every 6 months.
Their black color prevents algae growth.