Go and look at this link which is one of the best on chlorella I believe:
http://www.mercola.com/chlorella/index.htm

You are right but the point is "Chlorella plays a particularly crucial role in systemic mercury elimination because the majority of mercury is rid through stool. Once the mercury burden is lowered from the intestines, mercury from other body tissues will more readily migrate into the intestines -- where chlorella will effectively remove it."