Can someone give me a technical explanation, or a resource where I can read about why you would want the algae to have such good coupling to the air? There are several scrubber designs that would become advantageous if you could submerge your screen completely, and so I'm curious why you would not do this. Photosynthesis consumes CO2, I know, but is there enough CO2 in the air for the turbulent screen to really pick it up and bring it to the algae? I'd think just the opposite would be true, and any dissolved CO2 would off-gas into the environment and your water would be oxygenated in the process. Algae growth in your tank doesn't seem to be correlated to strong gas exchange - but only proximity to a light source.

Being able to simply build a thin chamber and fill it with water would remove a lot of the design challenges of trying to get even flow across your screen, prevent spray, use multiple screens with a single light source, and so on, so if someone can answer this it would be great.