tom, i know this has been discussed many times before. in this age of super measuring devices,wouldn't be it be nice for someone to come up with a (affordible) way to now how much co2,say at mid afternoon,you are injecting into tank. i'm burned on test kits,not reliable.not even pricey ones. allmost killing your livestock,i've found is too risky. there's gotta be a better way! 100$ would not be too much for a very reliable testing device when you have many tanks. regards,cornhusker