Also beware of using pH/KH of tank water to try to determine CO2 levels using that chart. That method only works correctly if the only buffers in the water are carbonate/bicarbonate based.
Water with phosphate buffers (for example) in it is very resistant to pH change, and the pH will drop considerably less when CO2 is injected.
If you want to know your CO2 level, use a drop checker with a 4dKH solution, or solution of baking soda & distilled water. It isn't perfect, but it is substantially more accurate than tank pH changes.