One more thing as to the CO2 concentration: In one of my articles I try to show that for aquatic plants to grow well they don't need to reach 100% growth rate, but they can grow at 30 or 50% and be in very good condition also. If you look at the "Dependency chart of external nutrient concentration on the growth rate of plants" in this article, you'll see that if we apply it to CO2, then for plants to grow at 100% they would need 26 ppm of CO2 (this number is just fictional), but for them to grow at 90% they need only 11 ppm of CO2, and for them to grow at 50% they will be just fine with 4 ppm of CO2. So tell me, please, what growth rate is "bad" according to you ... 30%, 50%, 70%? When do the plants suffer? If plants grow at 50% of the maximum growth rate do they already suffer? Do all the plants need to grow at 100% to be perfectly healthy? Or can they be healthy at 50% growth rate also? The answer to this question is crucial. Because if plants can be perfectly healthy at 50% growth rate, then they don't need as much CO2 as you may think! And did you know that most aquatic plants grow at 100% under 40 ppm of CO2? In other words, 40 ppm of CO2 is maximum they are able to utilize. If you read the article you will find out that once the concentration of free CO2 in water exceeds the critical limit of ~40 ppm, an immediate and quite dramatic inhibition of photosynthesis (growth) comes about. So do you still think that there is such a thing as suffering of our plants due to low CO2 in planted tanks where the CO2 concentration is higher then 10 ppm?