Actually this are advantages to using 1 dKH water: Yellow is an easy color for most of us to see accurately. At yellow you know you have enough, but possibly too much CO2. So, you increase the bubble rate slowly, until you get yellow after about 2 hours. Now, slightly increase the bubble rate, watch the fish and plants for a couple of days or so. If the fish cluster at the top, usually near a corner, lay on the substrate or lose their color, you have too much for the fish. If the plants improve in growth, or have more pearling with the increase, they may do even better with more. So, slightly increase the bubble rate again and repeat the observing and reacting until an increase shows no improvement in the plants. You are then as high in CO2 as you need to be. Maintain that bubble rate and all should be well, until you do a major pruning job, which will probably reduce the plants' need for CO2.
When I was experimenting with drop checkers I found I liked using 1.7 dKH water. That turns yellow at around 45 ppm, so you can shoot for "not quite yellow", and still have the ability to see "really yellow". I found that to be easier for me than judging various shades of green.
Last edited by Hoppy; 09-17-2013 at 05:05 AM.
Reason: added information