Halimeda is a calcified green macroalgae. It can be used for filtration, but is best suited for the display tank because of its great potential in aquascaping. It will not be eaten by fish or snails, making it ideal as a display piece. It does best when planted in a fine sandy substrate, but can survive in more coarse substrates as well. Despite its slower growth rate it will get some filtering done if placed in your display tank, or in your display sump.
This algae is capable of living under low-moderate light, it will grow strongest in moderate to high lighting. All macros present some risk of going sexual and releasing carbon dioxide into you aquarium. However, the risk of adverse ph changes from the release of carbon from this species is low. If you see the plant turn white with thousands of little green dots, then you should be concerned with the plant "going sexual" or sporolating. When the macro algae does this, it is usually heading down hill. This should not be confused with regular splotchiness and a general paleness in the algae that regularly occurs at night, or when the macro is in transport. Because this plant uses calcium to grow, you should keep your tank within 350-450 ppm of calcium for best results.
This item will cover both Halimeda monile and Halimeda incrassata. Halimeda incrassata is pictured. Similar looking species, both sprout up from the substrate and look like saltwater cactus. They both can appear stressed when trying to spread, as they spend majority of the energy ensuring the viability of the new sprout. Give them time to bounce back. They are not likely to become invasive as they can be easily pruned back. (Mostly because they don't creep along rocks, and grow from a single holdfast).