GreenWall, an algae CO2 scrubber. It can absorb and filter carbon dioxide (CO2). Water is pumped into the mounted tubing system for maximizing water flow and surface area for receiving light. When algae remove carbon dioxide during photosynthesis, they raise the pH by increasing the level of hydroxide. Therefore, a pH sensor is used as an indicator of photosynthesis activity by algae. The displayed graph indicates the pH level – taller the green bars, higher the pH level.