There are many different species of codium, but most have similar features. Ranging from dark to light green, the spongy algae has cylindrical branches that resemble fingers, which led to the nickname "dead man's fingers". Some species have a single holdfast, which will connect the algae to rocks, shells or hard bottoms. However, many hobbyists use other means to hold the algae in place, because it takes a long time to reattach, and some species never will.
Each branch has fuzzy filaments that give the algae an almost glowing outline when viewed from across the room. This is one of the algae that I always have in my display tanks, as it makes such a pretty and unique mark on any display.
Codium is not calcified, so extra calcium supplementation should not be needed. It does tend to collect tiny bits in it's fuzzy filaments, but with adequate flow, this shouldn't cause any buildup.
This algae has grown for me in so many different lighting situations, I will just say that the more light it receives, the faster it will grow. I've also noticed that the branches will grow more closely together and towards the surface in lower lighting situations. However, it's quite hardy and shouldn't be a problem for even the newest of keepers.