How to measure CO2 in a large planted tank

[Jeremy Shives]

Hey I've been trying to find a reliable way to measure my CO2 level in my 190 gal planted/dirt tank. I have an external reactor and the trying to figure out to best bbm for it. I know there's a lot of variables in determining CO2 because plants constantly absorb it but there has to be a way to measure it besides pH drop or growth rates or bbm? Or I am just searching for a solution to a problem I don't have? 

[Mmiller2001]

I use to take a fully degassed sample and pH it then shoot for a 1 to 1.5pH drop. I now do as @Pepere posted and simply drop by 1pH. With real time monitoring, it seems to be more than good enough.

[gardenman]

A CO2 drop checker gives you a broad guideline of your CO2 status, not enough, about right, too much, but I'm assuming you already know about those and are looking for something more precise. 

[Jeremy Shives]

I am but I did just purchase a drop checker for redundancy checking, I plan on measuring pH drop and the drop checker. I'll try other methods on the side but mainly those two. The post was trying to see if there was any other methods besides the common ones that I was missing.