Very interesting possibilities here, but I’m having difficulty understanding what is going on in the graph.
Just focusing on actual ppm and temperature, I’m seeing a range of roughly 7-11ppm in DO and a temperature range of roughly 23-26 oC, correct?
We are also seeing a dramatic increase in DO when CO2 is on. Is the implication that this is because plants are now photosynthesizing and not respiring? How heavy would you characterize your plant mass to be and is it a high-light setup? It would also be interesting to see what the pattern is if there is no surface agitation which, I assume, would give us a clearer picture of actual plant impact upon O2.
I’m also curious about the ppm readings, e.g.; at 26 oC, the maximum ppm (100% solubility) should be about 8.2ppm at sea level pressures, but you are recording 11ppm? Further, DO ppm should rise and fall inversely to temperature, but you are recording the opposite.
All of this, if true, leads me to believe that you may be experiencing super-saturation during photosynthesis (which can harm livestock) which is briefly possible with very rapid O2 infusion or am I just not reading this graph correctly?
Lot of questions, but since you have access to this instrument, it offers the potential for a great deal of insight. Not least of the possibilities would be to use your instrument to calibrate some of the O2 test kits, such as the Salifert kit.
As a side note: does your temp vary by that >5 oF every day?
Yes, the DO and Temp had the ranges you mentioned. We had the windows open all day so the temperature fluctuated just from that. It is possible to get DO above 100% saturation. This is pretty common in fast moving streams with a lot of aeration, but it is also possible in our aquariums due to the high oxygen production by plants. I don't plan on using this sensor for calibrating other test kits. It is actually getting deployed into a reservoir soon if we are unable to retrieve our sensors from the bottom of a research lake.
Plant mass is pretty heavy, and yes you see a drastic increase in DO because photosynthesis is producing oxygen. I'd say this 10g is Medium-High light. Compared to the people who have sumps/overflows, this HOB doesn't produce much surface agitation. I'm willing to bet my aquarium has lower overall DO at night than those with more agitation. I might get airstone to reduce the downward swing at night.
Here's a couple critical points recorded during the 24 hour period:
Highest Temp: 2020-09-12 @21:05:00, Temp:26.20, DO:10.73, DO Sat%:132.67
Lowest Temp: 2020-09-13 @07:25:00, Temp:22.81, DO:7.35, DO Sat%:85.35
Highest DO: 2020-09-13 @12:02:00, Temp:23.92, DO:11.06, DO Sat%:131.14
Lowest DO: 2020-09-13 @02:38:00, Temp:24.68, DO:5.97, DO Sat%:71.78
For clarity on the 2nd graph with the aqua and yellow portions, the aqua indicates the time blocks that CO2 is on, and the yellow indicates when the lights are on. You can see clear points in the DO where photosynthesis starts and stops.