Sunday, 10 Jan 2021, at 10:45, CO2PRIMARY emptied. This bottle delivered 112 hours over 61 days, an average of 1 min 50 sec per day. This is an approximate 33% reduction in the utilization rate over the last cycle. The last bottle change was 9 Nov, and on 13 Nov I changed the pH from 6.7 to 6.82. I have now upped it again, to 6.85, and am making an effort to lower alkalinity just a little. The objective here, as stated previously, is to throttle the system as much as possible without having to lower the light intensity. This is not only to reduce the net CO2 utilization, but also slow down the growth some. The lights are set for about 80% of maximum, and if I can maintain the general shadiness and favorable redox I believe I can remain algae free without attenuating energy input.
The total elapsed time numbers for emptying rate of the bottles has been historically variable. These are 20 lb, nominally, fully charged. How precisely this corresponds to an actual volume value is sketchy, but it shouldn't be surprising to see discrepancies in hours worth of controlled slow discharge. Since there are periods when vigorous aeration is used, the aquarium itself is variably lossy with respect to injected CO2. It is impossible to parse the initial deficit from the cumulative loss by just simple observation of elapsed time of discharge.
Toward the goal of ensuring low DOM, I am experimenting with activated carbon.
Today's numbers
pH: 6.79*
ORP: 531 mV
EC: 1120 uS/cm
NO3: 0 ppm
PO4: 0.47 ppm
Fe: 0.15 ppm
K: 45 ppm
GH: 52 ppm (2.92 deg)
Ca / Mg: 36 ppm / 16 ppm
KH: 6.69 deg
*Seven day running average; at 11:00 today pH-L is 6.85.
Generally, parameters are just a little down from Saturday. Yesterday, 11 Jan, I changed filters in high velocity loops 2 and 3, which resulted in around a 6 gallon water change, so no surprise here.