Here is a close up of the finished reactor cell working.  One little thing I found is that in such a tall narrow vertical tube the amount of water displaced by the bubbles can be quite surprising. My first attempt to fire this reactor cell up resulted in my ceiling and myself getting soaked. To address this I simply placed inline a 1.50 aquarium air flow control valve. This also is helpful with regards to maintaining pressure in the entire reactor if you need to service or harvest a tube.

And here you can see the completed system. It stands just over 2 meters tall. One of the things I love about this system is that you can connect all the cells to a single drain / harvesting system and refill the tubes all at once through the same outlet or each algae reactor cell can hold a totally different strain of algae. This flexibility in a cheap modular system is ideal for my projects and I hope for yours as well.