I'm growing some sativas that can get to massive heights, if you watch any of the greenhouse seed videos on youtube, one of them was about 9 feet. I don't have that much height in my rooms. I'm just using the 4 inch rw on top of a 6 inch to keep the root growth down, which in turn will keep their height down. As far as killing the algae growth, I had a cube show signs, so I ripped the infected areas, I didn't notice any growth under what I ripped off, so I think that did the trick. If you can afford it, grab some hydroguard, it helps kill microbes or whatever they're called, add that into your res.

__________________
My Green House Seed Co. Grow