Travis, Thank you. I did not seed the tray, algae (unfortunately) grows anywhere it finds favorable conditions. The purpose of the tray (or trough) is to provide a place for the algae that is "more" favorable to grow than in the tank itself.
I did replace that trough in the photo with a much nicer looking one, that one was a prototype. I also replaced the screen inside with a new one with new cement. So far there is no algae in the trough but also none in the tank. I am hopeing that when it starts to grow again (it will) it will only grow in the trough.
(now a disclaimer)
Guys, don't forget that my methods are always experimental and there are a lot of people that disagree with me. The trough can't hurt anything but you should be careful about following all that I do. I do have a successful, old reef but I also have a lot of experience and a few of the things I do I might not recommend to everyone with little experience like what I do with Clorox for example. Read everything you can and see what works in the long term for most people. I also do a lot of other "wierd" things to my reef that I would not tell anyone because, one, you would not believe anyway and two I don't want anyone trying.
Good luck and have a great night.
Paul