Many of you may be wondering how chlorella and spirulina are different. Indeed, the ingredients, and even the color and shape of tablets are similar. However, there're various differences between, Chlorella, which belongs to chlorophyceae, and Spirulina, which belongs to cyanobacteria. Rather, it can be said that Spirulina was newly introduced as a solution to the drawbacks of Chlorella.
Firstly, the drawback of Chlorella is that it is too small. The diameter is about 0.3 to 0.5 micron, which is only 1/1000 the size of Spirulina, so it is necessary to use a very complicated method of centrifugation for collection. In contrast, Spirulina can easily be harvested by filtration. Spirulina is far more suitable for mass production.

Secondly, Chlorella is a unicellular plant, which has a hard cell wall and is very difficult to digest. In order to be easily digested, it must be mechanically crushed or processed unnaturally, and there is a risk that the ingredients will be damaged.
On the contrary, since Spirulina is multicellular, the cell membrane is soft and easy to be digested without any modification. Therefore, the feces are less likely to turn green.
Please look at the table on the right. It shows the difference in digestibility between Spirulina and Chlorella quite obviously. Chlorella has a digestibility of 12.0% after 1 hour when untreated, and 58.7% even when the cell membrane is destroyed. Spirulina showed a very high digestibility of 80.0% without any treatment and 95.1% after 2 hours.