In learning about planted tanks and aquascaping I heard and read a lot about the importance of CO2 fertilization, how to get it right, not too little and not too much. In my recent experience I have discovered that the constant talk of CO2 lead me to leave out something very important for the health of any aquarium...OXYGEN! I had struggled keeping some fish (electric blue rams) and had chalked it up to my tap water being too hard (high Kh) and my CO2 too high. Other fish I found to be fairly inactive during the day, another behavior I attributed to CO2 intolerance. I wanted to keep my plants healthy and growing as well as stave off algae, so I kept the CO2 as high as possible without killing my fish, but algae was still a problem, growth still not optimal, and fish behavior in some species lethargic and inactive. In an effort to save my final blue ram who had begun breathing at the surface I placed an "emergency airstone" into the tank. Within ten minutes not only had the fish's behavior improved, but also that of other fish. I drew the conclusion that it was not CO2 intolerance, but rather a lack of oxygen. I have since began running an airstone 24/7. I have been able to turn my CO2 up, increase my lighting to what I had originally intended (I had reduced my lighting as low as possible to compensate for what i thought was CO2 trouble hoping that by slowing things down I could strike a balance) and everything has improved. Pearling is great, algae is nearly non existent, and my fish have never been better! OXYGEN, OXYGEN, OXYGEN!!!!! That was the true source of my troubles. I thought I would share this because I think many often get lost in the CO2 importance and fail to think of how O2 may play into someone's struggles with CO2. I plan on sharing much more about my experience with this high tech tank in a future issue of aquascaping world magazine. I just couldn't wait to share this because of the huge turn around I've seen, hope it is useful. .