The mist still "dissolves" in the water. Use the drop checker in combination with watching fish and plants. Be careful and go SLOW. Fish will take a bit to adjust and taking a few days is much safer than going fast.
But the idea with mist isn't dissolved CO2. It's that CO2 is more easily absorbed by the plant from the tiny bubbles ( Don Ho anyone? ) sticking to the leaves than from the plant having to absorb the CO2 that's dissolved in the water.The CO2 from a mister still dissolves in the water, but generally not as efficiently as CO2 in a reactor. So, if you switched from a reactor to a mister you would probably have to increase your bubble rate to get the same dissolved CO2.