Chlorella is nature's "activated charcoal" and can be taken daily to help detoxify unwanted metals from the body. It is especially popular in Japan, and may be contributing to why the Japanese live so long.
In the past chlorella was pretty much only consumed for these detoxification properties, but chlorella supplements today are far superior. With the invention of technology to crack the chlorella cell structure, our bodies are able to digest significantly more of the nutrients inside.
These nutrients include CGF (Chlorella Growth Factor), which there have been many studies on. It supports the immune system and healing, among other benefits.
In 2007 they also started growing chlorella in a sterile environment, in tanks, which allows them to be grown without any pollution. Chlorella grown outside has measurably higher levels of heavy metals and there is always the chance that cyanobacteria is introduced into the pool, another "algae" that you would not be able to easily distinguish.