The plexi is about 1" down from the water line - basically 1" below where the water would flow out of the tank. AC is simply an abbreviation of the filter's manufacturer, Aqua Clear.
Since chaeto doesn't go sexual, I only run my fuge light during the day while my tank lights are on. I'm sure if I left the lights on 24 hours a day, the chaeto would grow twice as fast as it does, which is pretty darn fast already. I have to prune it back every three to four weeks because it fills the whole chamber.
The Jali light came from here.
http://www.petsolutions.com/Jalli+11...I-C-33-C-.aspx