I in fact built this tent using white pvc as described in the link and it is covered with white visqueen plastic. I have had the plants in there for about 2- 2 1/2 weeks now and didn't notice any problems until after the second week. This is a bummer. It started to happen after the addition of thee 1000w which may have made the temp rise, releasing some chemicals. I hope it's not this.
Thanks though, That is the best answer I've gotten yet. any other ideas???