You don't need to know anything about the CO2 saturation levels, that's for growing freshwater plants in a CO2-dosing environment. What you want are the pH and hardness numbers, those will tell you where you're at, gives you a starting point. Then you go from there. pH being out of whack can not just mess things up, it can kill. Kills fish much more quickly (and completely, too), but it does bad things with plants, especially indoor-grown plants.
As for the hardness, you may need to filter or use storebought water. I live far from stores and the filtration I was using was insufficient for the amount of water I need, so I saved up and dropped for an RO/DI system. Before that I was boiling the water to help bring the hardness down, which helps you control pH much better. See, it's that hardness that keeps pH "stuck", so to speak. That's called "alkalinity" and it's a term that refers to the water's buffering capacity, or resistance to pH shift.
So, mostly you want to know how hard the water is that you're using for feeding, and you must know the pH so that you can ensure the plants can utilize the available nutrients. I don't post the pH--nutrient charts because not a one has shown any veracity, they seem to be more guesswork than anything else. I go by growers' advice.
You never said what medium you're growing in, at least not in this thread, or I can't remember. Medium and style (indoors versus out, chemical salts versus organic) dictates in large part how you have to work this and how much you have to worry about a given parameter.
If you're in soil and indoors using some chemical salt-based fertilizers then you want your feed solution in the mid-6 range as a general rule of thumb.
