As it is usual with ALL plants, the carbon is usually used to build plant matter. So the algae in the cells are certainly reproducing, which brings the question of algae growth management. This system can not operate as a closed loop cell, it must continually have water cycled in and excess algae cycled out.
Agreed that's the likely explanation. My objection is that the article elides this, and is false on its facial claim that "its only byproduct is water".
