Today's numbers
pH: 6.81
ORP: 439 mV
EC: 1050 uS/cm
NO3: 0
PO4: 1.23 ppm
Fe: 0.32 ppm
K: 40 ppm
GH: 64 ppm (3.6 deg)
Ca / Mg: 42 ppm / 22 ppm
KH: 7.98 deg
All good except NO3. Nitrate has been coming in at 0 for quite awhile now with infrequent small bump-ups. After Tuesday's 10% water change I am certainly facing a deficiency condition, so I have added some KNO3 supplement. At this point I am closing out a month of charting NO3 and PO4. I have been feeding liberally, including fresh frozen every day for the last ten days. The two certain things are that 1) the nutrient that is present has been all autochthonous, deriving from the fish (i.e. fish food), and 2) the streaming water change regime is diurnally constant. There is sufficient variability in other environmental conditions that nutrient concentrations do fluctuate somewhat, but causality is obscure. Insofar as is concerned the idea that autochthonous nutrient is a sufficient source for the plants, the numbers are showing that orthophosphate persists in the system, but DIN does not. It may be necessary to supplement allochthonous KNO3 with daily dosing just enough that NO3 can be made to persist. I will add this manually for a time until I can get an idea of the appropriate dose rate.
In any case, I can state that generous feeding of the fish is possible without lapsing into a eutrophication trend.
The NeoMag and aragonite in pump loop #1 are supporting the GH. Upon opening the filters, I took the opportunity to double the NeoMag; I am interested to see if this will increase the Mg in the water column. I suspect supplementing MgSO4 will need to continue to keep a desirable Ca:Mg ratio, but we shall see.
I am still not seeing any problems with the pH increase. At the specified KH the CO2 ppm is in the mid-thirties. Except in the normal periphyton, which is very slow, there are no algae. Again, I attribute much of this to long-term maintenance of stable CO2, trophic status free from DOM, lean in nutrient, and rich in oxygen. I have the lighting pretty well turned up, and while there is benefit of shade from the canopy of large-leafed plants, I am not so leery as I used to be about the relationship between energy intensity and nuisance algae.