Making the hobby into a chemistry lesson and fretting over things that aren't easy to change, just takes some of the fun out of fish keeping. But, if that's your thing, then fine.
I would hardly call my advice a chemistry lesson. The OP has taken KH/GH readings, so maybe I'm guilty of assuming that he is interested in learning about his water parameters. Sure, you can do the whole Walstad thing and let nature take it's course and maybe get lucky and grow out some healthy plants without a lot of work or thought put into it but that's not what the question was about. There is apparently a concern about his calcium levels and I recommended a GH booster. I also recommended some baking soda to raise KH levels because it's not doing any harm, especially with that particular substrate lowering it down to 1 degree until it loses it's buffering capability.
I didn't throw out formulas and whatnot to show why low KH (1dkh or less) has such a limited amount of dissolved CO2 and why simply raising KH has nothing but a positive effect on such potential CO2 levels. Apparently the OP has taken the steps to raise KH with the use of calcium carbonate.
0 KH water (RODI) CO2 levels = .44 ppm Water with a pH of 8.2 and a KH of 18 = 3.4 ppm This assumes you are creating good surface agitation for gas exchange.
Me knowing what my parameters are and being able to make a few simple changes to get positive results is
my idea of fun. I like to tweak things, it keeps me engaged and keeps things from becoming stale in my life. So yeah, it's my thing I guess. What isn't my thing is having someone trying to discredit my advice in a passive aggressive way because they think that their way is better. You are also assuming as much as I am that the OP cares one way or the other. I'm not saying your way is a bad way to keep fish/plants. People have been doing it this way for ages because it just works. I tend to think more along the lines of this mentality in my outdoor gardens. Feed the soil, let the soil feed the plants. With aquatics, I take a more technical approach as mentioned. The OP can decide what method suits them best.