The following images and info was gathered by Deyan (Dido on www.aquariumbg.com
, contest pages are here
) a Bulgarian guy using his DIY microprocessor. The graphs don't show anything revolutionary different from what we already know but it's very nice to see everything graphed like that. Also on the second graph there is proof for gradual exhaustion of the CO2 - something that I personally thought happened in less than one day. The first graph
shows the moment of the CO2 bottle running out on Jan. 14 about 4:00 PM. The controller was set to maintain pH=6.2 and as we see up to that point the pH was properly maintained. The lights come on at 12:00 and are turned off at 21:45. It's interesting to see how the CO2 drops (pH goes up) in a straight line between midnight of the day the CO2-supply was cut off and noon the next day. I suppose that's the time when the plants were releasing CO2 and I'd expect that the pH increase should be slower due to the acidic nature of the CO2 coming from the plants. But that is not so.
The portion of the graph between noon (lights come on at noon) and 10:00 PM shows an even faster pH increase. As expected the light stimulates the plants to use CO2 and as a result the pH increases sharply.
After peaking at about 7.3 the pH drops abruptly once the lights go off at 9:45 PM. Note how at 10:02 PM there is a sudden drop of pH due to the release of CO2 by the plants. It happens FAST! The second graph
shows the pH fluctuations in the span of 3 days. As expected when the lights are on and the plants consume CO2 the pH increases. And when the lights are off the pH drops because the plants release CO2 at night. What's interesting is to note how pH increases over the 3 day period. The first day the highest pH was 7.26, the second day - 7.48, and the third day it's about 7.5. It appears that the tank is gradually exhausting the amount of CO2 over time - on Jan 16 we had more CO2 in the whole system than we have on Jan 18. I personally thought that the pH hits a peak and stays there the first day after the CO2-supply has being stopped: The third graph
is a magnification of one of the pH peaks. It shows that the pH increase (the CO2 usage) is dependent on the light. Since the lights come on at noon and are shut at 9:45 we can see that the connection is straightforward - when the lights are on CO2 is being consumed and the pH increases. The opposite happens during the period of darkness between 9:45 PM and noon the next day. What's interesting to note is how fast the CO2 is being consumed (pH increasing fast when the lights are on) in comparison to the CO2 being accumulated (duing the period of darkness). Maybe someone will explain that difference, I can't: