Liquid CO2, such as Seachem Excel, is glutaraldehyde (glut). While it is used as a carbon source and an algaecide in planted aquariums, there are some plants that cannot tolerate it.
Glut is known to kill Anacharis, Hornwort, and Vallisneria (vals) when used at normal dose. Higher dose or spot dose can affect other plants.
While the list of plants is few, it's best to double check that the plants you have can tolerate glut before using it in your tank. You should also double check any sensitive fish and inverts just to be safe.