You dont really need to monitor it just start by adding the bottle dose daily then slowly increase to 2x dose over the next few days
Easycarbo will break down in the water and will be gone within 24hours
You cant measure it with a dropchecker
Vallis, some mosses, and a couple of other plants dont like higher doses but most plants.
I believe you can get test kits for it but they are specialised and probably very expensive
Stop worrying and start dosing, watch your flora & fauna and don't overdo it