Just to answer some of the questions that i read...
There is no venturi on this setup, as they only cause restriction on the input to the pump. A venturi is used to allow a pump to "pull" air in on its own, however, with the amount of head pressure that was being put on the pump, it would never be able to pull air in. So, the T fitting allows for maximum flow into the pump, and the introduction of air with out constricting the flow of water.
Fiber glass would be great as you is alot easier to mold into the shapes. I know someone else built one body and dome out of it, and it looked like it worked great.
The dome was made by me, however, i would buy one next time, as you can buy it pretty cheap, and it would be completely uniform, and come with a flange that would allow for a better attachment to the drum. With a flange, i could have drilled holes into the lid and used neoprene to make a gasket.
The phyto reactors have been brought up many times, however i agree that they may be to flimsy to support the water pressure at the bottom of the cylinder. I am not positive about this though as i have never seen one in person.
The needles are made up of 1/8" acrylic rod.