The images don't tell you what is an adequate level of CO2. They tell you what the pH is. If you have low KH, as I do, the pH needs to be lower for adequate CO2 than it was when I had much higher KH. So, the color would be different for the two cases. Where can I get Bromothymol blue? I just bought one of the ebay devices - the cost is low enough just to play with.
Why wouldn't this device work equally well if you loaded it with distilled water with a tiny bit of baking soda to get some carbonate in it? Then, wouldn't the CO2 ppm in the device be the same as in the tank water? And, with "ideal" water, of known KH, the pH would truly represent the ppm of CO2 in both the device and the water. I don't see the flaw in doing this. |