Joe, i believe you are missing my point. i tried several other plants in that tank which suppose require less co2 and they did terrible but some how HC did well, what does this tell us? HC is good indicator of CO2?
To me it proves HC is adaptable if provided with other favorable conditions, same thing with Raj's pantanal. But in a co2 injected tank, both are very sensitive to poor co2.
By poor I mean low or unstable. Up and down levels are a big problem because the plant stays confused how to delegate their inner resources. Like producing rubisco to deal with low levels, which is an expensive enzyme to make.
Say a tank has just enough co2 when it's freshly trimmed, but two weeks later when biomass has doubled and circulation isnt what it used to be, the plants have to switch gears which causes growth to stall for a while. Then about the time they are adjusting to lower levels, boom, here comes a good trim and cleaning and co2 is back in abundance again. Well the plants start adapting to that... again. Rinse and repeat.
That is what's meant by unstable co2, and some plants tolerate it better than others. The ones who dont tolerate it well can be described as "good co2 indicators."
Whereas in a low tech aquarium, the plants can adjust with high rubisco (etc) and cruise a long fine because nothing is really changing. But that's not the same as tolerating "poor co2" in a co2 injected tank.