Santa monica, I already know you are going to hate the thought of it... but what if this guy used a wheel design (pretend it rotated reliably).
I dont know what you know about this eco-wheel type stuff, but thinking about it I have a feeling you will say it is not enough... but entertain the thought for a few seconds, then shoot it down.
quick calc this guy would need a wheel the size of a 5g bucket.
16 paddles.
all 3.5"x13 to 14"
this divided by 2 for the flat algae surface area gives you about 364 to 392g of algae scrubbing.
Next is lighting. with this design, only 1 or 2 lights need to be on it focused on the top area only = lower electric bill?
Now what I am guessing you will say is that the watts of lights needed for the high bio load will not be met with the wheel in and out of the light each rpm?
Any thoughts on if this will work... so I can build it and make it work!