Some people insist that you can’t calibrate the G6, and I feel like it’s a carry over from previous experience, or maybe that they learned different calibration habits on the previous generations of sensors and you need different habits with the G6? You really gotta try not to come into the new system with preconceived notions because you’ve read things. Remember, mostly people only post when they’re having problems. It in no way indicates that the majority of users share that problem.
As a Control-IQ user who trusts my life to sensor accuracy, I DEMAND accuracy from my G6, and calibrate as necessary… Which honestly is rarely, but I do check occasionally. I have no problem calibrating when necessary and have never seen this “fried sensor” outcome, though it is definitely possible to confuse the Dexcom or calibrate incorrectly The general rule of thumb is to only calibrate when your BG is steady/flat. If you’re rising or falling, it will definitely throw the subsequent readings off. It’s possible your BG had finally risen out of that low and your sensor hadn’t caught up yet, since there’s a lag between actual BG and sensor reading. If that were the case, it would definitely explain the high readings later on. It would have been more accurate to calibrate with a fingerstick that was 15 minutes ago, but that’s not likely possible, hence you really don’t want to calibrate when fighting lows, highs, or recently having eaten, as it’s not likely you’re data is really flat, no matter what the graph displays. The other calibration rule is that you have to be conservative in the changes you make. It’s really only those who restart sensors that have to worry about this (as they can easily come back 100 mg/dl higher than true after a restart), but you’ll likely get an error if to try to adjust it more than 50%. If you have to make a BIG calibration, you’re better off splitting the difference between two different calibrations spaced at least 15 minutes apart. If you’re in one of those can’t calibrate yet ruts, just turn the automation off and control your insulin manually until you are able to give it a good calibration.
Some people find they have awful first days on the G6, then the accuracy falls back in line for the rest of their session. They benefit from “pre-soaking” the sensor. Meaning they insert the session long before they actually install the transmitter and start the new sensor. It just sits there unused for however long they deem necessary to ease the first day blues, usually 6, 12, or 24 hours. You might be one that needs to try pre-soaking if your first day’s readings are erratic, not just off.
All that said… Not all sensors are created equal sometimes they just suck. You might just get a bad sensor, and occasionally an entire bad box. Tandem has a great replacement policy with Dexcom, as they demand accuracy for us, too. If you’re having sensor issues, call Tandem, not Dexcom. They’re very liberal with sending replacement sensors. Basically if you ever need to calibrate 3 times in 24 hours, Tandem will send you a new one. And if you’ve got a bad one, you’re thing to be doing enough fingersticks that this is easy to prove. Also, they replace if the pump tells you there was a sensor error or if more than 3 hours has passed in 24 without data at all (pump reads “—” where your glucose should be). They’re also generous if you get annoyed and just replace it yourself without directions to because you were frustrated. 
and corrected. I think I read here that you can only recalibrate a sensor a couple times before you fry it. Is that true?