Caulerpa may look attractive in saltwater aquariums and refugia, but it bears an ugly downside: a tremendously invasive growth pattern. The seaweed’s ability to strip excess nutrients from aquariums makes it popular with some aquarists, but its prolific growth leads them either to discard the plant or routinely thin it.
This is where the problem lies. Releasing Caulerpa or aquarium water into gutters, storm drains, or other waterways can cause a Caulerpa invasion in the wild. As in tanks, Caulerpa can quickly overcome native species, making it one of the most invasive species in the world. California has banned nine species of Caulerpa, including feather Caulerpa and grape Caulerpa.
The good news is there are alternatives that work just as well, such as Chaetomorpha and Halimeda. If you have Caulerpa in your system, properly dispose of it by freezing it and any attached materials in a bag for 24 hours and placing the bag in the trash. Dispose of aquarium water into a sink, toilet, or shower, all of which lead to water treatment plants, not waterways. This will prevent Caulerpa from reaching the wild, causing a costly infestation.