How can anyone be sure of any analytical measure...for example world class pH meters used daily in my industry are calibrated twice daily. Same model meters & same model probes can and usually will vary +/- 0.2 pH units for any given measure of the same sample within the same day.
Nature is all about balance and adaption right, so how do we know where that balance lies for us at home that cannot dial in our pH or know for certain our KH in order to get the CO2 well balanced. I have the Milwaukee pH controller for my CO2 system now and I calibrated it next to these world class meters at work and obtained the same values at pH 4, 7 & 10. I was impressed with their equipment. After I had in controlling my CO2 regulator for a week I went to recalibrate and it was off calibration by 0.2 units. That to me should be sufficient. I recalibrated and assume the value I'm ready is accurate. I'm sitting on pH 6.7-6.8 with consistent KH titrations of 7. I've only been doing this a couple weeks but that should be the right balance. Please let me know if I'm doing something wrong here. I want to "get this down pat", understand it, and help others learn it.
I like the riccia stone concept. Could you elaborate ?
What are our true "degrees of freedom" (assuming all we have a pH meters, pH & KH test kits) when trying to dial in & understand our respective relationships to pH, KH, & CO2 ?
I use a pinpoint 0.01 pH probe/meter, these are pretty good, plus minus about 0.05 pH units to the reference (4.001, 7.001). Stray current can depress the values, many folks claim they have plenty of CO2, and do not due to such issues. Or they may have non carbonate alkalinity as well as bicarbonate.
Picking up another sig digit will help when using/measuring and recalibrating to check. That's why we use them.
Unlike you, I use a pH meter, and do not use a ph Control function, so my test works better at that point in time, whereas any change to KH or pH probe drift will change the CO2 delivery as well with your method.
Since my system is merely dialed in using the pH meter, the flow rate from the CO2 system is golden, eg, it's stable regardless of what the KH issues are/or the pH probe says a few hours later etc.
The Flow rate, delivery of the CO2, which is what we want for plant growth, it being added in a stable manner. A dual stage reg, a good solenoid, check valve and high grade vernier handle valve will provide extremely stable CO2 flow rates.
I will leave the pH meter on and watch time to time.
But if I want to be sure, I'll recalibrate it, same with measuring the KH again, and then using the dry ice in a sealed flask with aquarium water(I purge the CO2/O2 out using N2 gas) and then a known reference 2 KH solution.
Dry ice melts/dissolves fast and I have a known mg/l solution of CO2.
I think you should be able to get to within 1-2 ppm using this method.
But this is used only after the fact, post hoc, after you have a good excellent plant growth reference point. This presents a problem for most aquarist, since they come here with the growth problem already, they have no control or reference point to begin with.
Sort of like a pH meter without any way to calibrate things, hard to use no?
Same issue with CO2 ppm, we have few methods to confirm our methods.
So we can attack this using another method, a specific easy to grow plant that is visually an aggressive pearling weed: Riccia.
you get this after 1-3 hours when it's down on the bottom of the tank:
What is "Plant Pearling"?
You are in good shape as long as the fish are healthy, happy, behaving well.