Note, test kits like that and others, (pH meter + KH = CO2) are all relative measures and have a certain amount of issues.
They rarely will ever over estimate CO2 ppms, they will often times tell you that there is more than is really the case.
Keep this hard learned lesson in mind always.
I like to use Riccia attached to rock.
If it pearls well after 1/2 the light cycle, then my CO2 is good.
Less than this, not so good, likely need to add more CO2.
Also, make sure you have enough current also and surface movement, not enough to break the surface of the water.
This adds O2, which allows the fish to breath easier.
Since CO2 and O2 are both functions of respiration, this is easier on fish.
Yes, you degas some CO2 this way, but...........it's easy to add a tad more CO2 to make up for that.
IMO/IME, a pH meter + a Lamotte Alkalinity test kit and pH/KH/CO2 table is better than the DC's. Plants and experience/eyeballs are the best over all.
Watch fish and only adjust slowly then observe fish, plants etc.
Large water changes will also give you an idea of the max rate of growth due to CO2 for your plants, watch the tank after a large water change.
Regards,
Tom Barr