The main reason i added Chlorella to my diet was because i used to have heavy metal toxicity which was a large cause of many of my health problems.
Also because i don't tend to use synthetic multi-vitamins/mineral supplements, i try to use wholefood natural nutrient sources whenever possible. So instead of a multi-vitamin i blend up a few green powders such as chlorella, spirulina, wheatgrass, nettle leaf, some amla for vitamin C, seaweed/kelp powders for iodine and minerals.
I regularly weight lift/bodybuild so i need to make sure i get adequate and slightly higher than normal levels of some nutrients. In particular both chlorella and spirulina are great sources of protein(amino acids) by weight.
Low energy can be caused by multiple different issues, chlorella and spirulina will supply the nutrients the body needs though.
Amla & Vegan Blog