Hairgrass

Eleocharis acicularis — commonly called dwarf hairgrass — is a sedge in the family Cyperaceae, distributed widely across temperate to tropical regions of the Northern Hemisphere. Its needle-fine, upright leaves spread horizontally via runners to form a close-cropped, lawn-like carpet across the foreground substrate. Adequate light is essential: insufficient illumination causes upward elongation rather than dense lateral spreading. CO2 injection dramatically accelerates both horizontal spread and overall vigor. Fine-grained sandy substrates allow runners to penetrate and spread with particular ease. Broad water-parameter tolerance makes it relatively resilient. Regular 'mowing' — trimming the mat to a uniform height — stimulates the production of new lateral growth and increases carpet density over time, ultimately yielding the flawlessly groomed foreground for which it is celebrated.

Source: Wikipedia (CC BY-SA 4.0)

Root tabs, CO2