Hmmm, one guy who was watching my vid about Fluval Edges had an interesting remark - this tank has the watersurface almost completely covered by glass, so the gas exchange might be very reduced. It's pretty obvious, after he said this, but I didn't think about that in this way before. What you wrote above might be an evidence that these tanks indeed have problems with gas exchange... Not every tank. But many of them Actually, most planted aquariums at the whole show were scaped by not more than 10 people, I think, if not less. Most of them we know from this Forum, BTW OK, and now two new videos from InterZoo 2012: Dähne Verlag and JBL (planted nanoaquarium and large tank with discus and arowanas): Tropica (planted aquariums arranged by aquascapers from UKAPS): Enjoy!