If you want, you can use the pH/kH chart to backtrack and figure out what ppm of CO2 you have. If you do this using a drop checker (known kH) it should be much more accurate than using a pH and kH test kit with tank water.
For example, you'll be using the 4 dKH row. Look at a pH test kit card and pick the color that matches your drop checker. If it's solidly green, then you have a pH of 6.6 or so, right? On that chart, a KH of 4.0 and a pH of 6.6 is 30 ppm CO2 which is the "ideal" level.
Of course, some people use a 5 dKH solution in their drop checkers, so when theirs turn green (at pH 6.6) they have closer to 40 ppm CO2.
In another thread of yours
you said that your new drop checker turned pretty yellow-green, and you were concerned about your fish. Looking at the pH test kit card, I'd guess you had a color similar to pH 6.4 or so? That would mean your CO2 was at 47 ppm, or at least in that range.
Of course that raises the question of what levels of CO2 are safe for fish. I think I remember Tom Barr saying he'd seen some evidence that it's not the absolute level of CO2 that suffocates fish, but the ratio of dissolved CO2 to dissolved O2. You can apparently raise the CO2 pretty high as long as there's enough O2. Since your plants were producing enough O2 to bubble, the water should have been pretty O2-rich.
I'd personally suggest being more conservative than that, but that's just me. Watch your fish and make sure they're healthy, and try and keep the color of your drop checker somewhere between 6.4 and 6.8 on the pH test kit chart. That's what I do, at least. As long as your fish are acting healthy you're doing ok, right?
I guess the real
point is that I think you're overthinking things. As Tom Barr says, they're just pond weeds anyway.
Actually, this might be getting into the territory of unwanted advice, but from reading your threads, it seems like you might be overthinking and overcomplicating a lot of things in this hobby.
I guess some of it is
complicated. But I still think you'd be happier if you chilled out, trusted yourself more, and had more fun.