Starting on G6 and Basal IQ

Hello everyone,

I just moved from the G4 to the G6 on my Tandem pump this week and have a few questions and concerns:

  1. I’ve had to calibrate twice this week. At about 24 hours in, I was dealing with a stubborn (although fairly mild) post breakfast low. Right before lunch I tested and my BG was 114 and my CGM was showing 75. I calibrated and my sensor seemed to run very high for the next 10-12 hours. I could tell because I was still wearing my last G4 sensor which has been one of the best I ever used. Did I make a mistake calibrating? Should I just have ignored the difference and dosed off my finger stick?

  2. I woke up at 7:15 this morning and my G6 showed 174. My G4 and a finger stick showed 135. I recalibrated again :unamused: and corrected. I think I read here that you can only recalibrate a sensor a couple times before you fry it. Is that true?

  3. I expected Basal IQ to be a nice add-on but I’ve turned it off. Shutting down the basal doesn’t seem to prevent lows just pushes them back a bit and then correcting them gets complicated. Once I treat the low - and I’m very conservative treating lows - usually 4 grams if I’m above 65 - I begin to roller coaster. It seems that the only way to make it work for me would be to go into pump history and calculate the missed basal and then reduce my quick carbs for the reduced basal. That seems like a lot more work for not as good results. Am I missing something?



Maurie, I don’t have any concrete suggestions but I’m three months in on the G4 => G6 transition and I understand the challenges you face. I’ve been trying various experiments and have learned a few things.

Over-calibration of the G6 is a real thing and it’s hard to know when to do it in order to place the algorithm on the right track and when to leave well enough alone. Many people have developed personal rules of thumb for when to calibrate and when not to but I’ve found some hazards when trying their conclusions.

I also use an insulin delivery system informed by the G6 sensor readings. I’ve chosen to strategically put my system into “open loop” when I know the BG readings are garbage.

My current sensor is my most successful one so far and I started it without inserting a code, the so-called “no-code” option. The first 12 hours were miserable with inaccurate numbers and false alarm fatigue that interrupted a night’s sleep. It then settled in and has produced “G4-like” dependability. I’m on day 16 now. I woke up this morning with the G6 @ 92 and my fingerstick read 88.

For my next sensor, I will insert it 12 hours before I will place it into service by mounting the transmitter onto the sensor. I will try to use a code this time and see what happens. I don’t mind the required calibrations every 24 hours and a few more at the start. Avoiding calibrations seems to be a big prize for most users but for me, not so much.

If I get to the 10-day mark on that sensor, I will restart by removing the transmitter for 20-30 minutes and restarting as if it’s a new sensor. At that point, I will do a “no-code” start as suggested by @MM1. She says that the original code provides good guidance for the first session and that using the “no-code” regular calibrations required for the second session will work better. I’m persuaded by that and I’ll see what happens.

All of this learning new tactics makes me nostalgic for the G4 but that sensor is no longer available. Most people do very well with the G6 but there are a significant minority of us who struggle with it. I think our challenge is to find what works for us and then take action on that basis.

Good luck with things! Diabetes always demands its due and this is just the current iteration of that challenge.

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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. :grinning:


I have learned that calibrating the g 6 is a waste of time in that it always reverts back to the original internal calibration.
I have found that if my sensor is not accurate past the first 12 hours then it probably is a bad sensor or bad install.
And I just change it.

That has not been true for me, but I wait 10 minutes between calibrations.
G6 will close the gap in 2-3 readings rather than immediately, so 2nd calibration may not be needed.

I think the idea that you can overcalibrate the G6 to the point it will no longer work is a bit of an urban myth. I asked Dexcom about it twice and they said no, it won’t, but they didn’t recommend it because it likely won’t improve the data stream and may degrade it.

As for me, I was totally frustrated when I started on G6 having been extremely pleased with the G3, G4 and G5 (Seven+ is another story?). I was about to bag it until I tried presoaking for 12 to 24 hours as others have mentioned. Now I calibrate once at startup and a couple times, if necessary, in the subsequent few hours. For me it will invariably be off at startup because of presoaking. The algorithm is looking for a signal from a freshly inserted sensor while one that is presoaked is several hours old.

Now I’m a happy G6 camper!

Thanks Terry - I’m going to try a few sensors before experimenting with soaking and restarts. That’s also the reason I stopped the Basal IQ - I’m going to keep things simple and try to learn one thing at a time.


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@still_young_at_heart. Maurie, I have several thoughts.

  1. Are you calibrating because the system requested a calibration or are you doing a cal because there was a difference? Suggestion: if you detect a deviation between a finger stick and a G6 of more than 25%, wait one hour and then repeat the cal. If it is still off by >25% (more than 20 mg/dL with BG <90), then treat this as calibration #1 & call Tandem tech support and report if the next cal is still off.

  2. Read about pressure hypoglycemia reporting. If you sleep on the CGM sensor/transmitter, your weight presses the interstitial fluid away from the sensor, body cells digest the sugar in the area & it is not replaced until you roll over. In the mean time, you get a low CGM alarm which disturbs your slumber. Suggestion: Watch out for the false pressure hypos & read more about them.

  3. BIQ is not designed to slow basal insulin when the CGM detects a dropping BG 20-30 minutes in advance. Connect your pump to mobile:t:Connect and follow the data. Turning off BIQ will not impact the CGM calibration roller coaster you are describing.

Bottom Line Suggestions:
A) avoid the calibration circus as best you can.
B) turn BIQ back on and give it another chance.
C) if the calibration circus starts, assure it is not pressure related, then work with the Tandem/Dexcom tech support. It may be a bad sensor.
D) Consider upgrading to CIQ which will watch HIGHs and LOWs. I have been on CIQ since January 2020 and it works great.

Let us know what you figure out. It is how we all learn.

Did basal-iq work differently when you used G4 ?

I just started tandem C-IQ, and still trying to work out the zero basal rebounds.

Basal-iq never worked with the G4, it was first introduced with the G5. Tandem did sell a completely different pump that linked with the G4, but it was only a display, no pump automation connected with it.

Are you rebounding higher than target after a basal suspension without eating any carbs? Do you find the basal suspension too little to avoid the low or too slow, and feel like you still need to correct with carbs? Both of those are indications that your correction factor is set at too low of a number. It’s programmed to withhold too much insulin. I swear, that’s the biggest factor in making Tandem’s algorithms behave for you. That one silly little number makes or breaks everything. I feel like all the other settings (at least with Control-IQ, there’s not as many settings with Basal-IQ) are just used to set delivery limits. I don’t use the bolus wizard anymore, though, because I feel that I need a more aggressive number for corrections than what I need for pump automation.

Getting better, as I’ve tweaked the settings. Trying sleep off while I adjust, so I get bolus correction instead of micro basal bump overnight. My midnight snacking doesn’t help !!

Thank you - If I insert a new sensor 12 hours before I start it up and I’m using my transmitter on the sensor that is finishing up, do I just leave the top open/empty?


I will try to avoid calibrations on the first day unless the results are whacked and likely to keep waking me up at night.

I may give B-IQ another chance after I’m more comfortable with the G6. I tend to run 70 or below less than 1 hour per day for all episodes and rarely hit 55. I’m beginning to think if it ain’t broke don’t fix it. I’m not that cognitively flexible :slight_smile:

I never understood the science behind pressure lows but I sleep on my back for other reasons so thankfully, they aren’t a problem.

Control IQ isn’t in the cards for a while. I run tighter than the Control IQ targets and my trainer suggested that I might end up fighting with the system, I’m trying to keep things as simple as possible and doing what I’ve done for the past dozen years on my pump just feels simpler than learning a new system right now.

Thanks for all your help,


I leave it empty, but others cover it using various methods. I’ll let them share their thoughts. I haven’t found it necessary.

Good luck!


There has been a lot of good discussion of G6 calibration.

Let me make a couple of comments on B-IQ … which is the first generation of commercial closed loop automation.

Looking back, robotic closed loop automation got its start in the 1950’s and 1960’s. After 60-70 years of effort, can a robot catch a fly ball as well as Willy Mays did in the 50’s and 60’s as a NY/SF Giant? When will an autopilot be able to pull off what Capt. Sully Sullenberger did during “the miracle on the Hudson”?

Skilled humans are REALLY good at complex tasks. We have some T1D superstars here who run circles around what B-IQ or C-IQ can do. It sounds as if you may be in that category …

Me? I am not … with a CGM and pump alone, I struggled to get to 60% TIR. With B-IQ, that increased to 65-70% TIR. With C-IQ, I’m at about 80-85% TIR. So, with all that technological help, my numbers still stink compared to many of you …

I have learned two rules of thumb when using B-IQ (or the low-preventing part of C-IQ, which is not exactly identical to B-IQ, but, to me, behaves the same):

  1. After looking at my current CGM trend reading and trend arrow, I next mentally calculate the ratio of IOB to basal rate (BR). If BG is falling and IOB/BR > 2 hr, then B-IQ is likely only going to be of limited help. If IOB/BR is significantly bigger than that, it really can’t do much. For example, if I have 3 u of IOB and my BR is 0.5 u/hr, it would take 6 hours of zero basal rate to not inject the amount of basal that I already have on board. In that case, dropping BR to zero isn’t exactly “slamming the brakes on” an impending low.

  2. When B-IQ does work well … which for me is low-IOB and comparatively slowly dropping glucose levels, if I do need to eat carbs, I eat about 50% of what I would eat without B-IQ to avoid the rebound phenomenon you describe.

While you may be providing better feedback yourself without using B-IQ, these two things have helped me get the best performance out of B-IQ.

Stay safe,



Agree 100%. B-IQ is most effective with little or no IOB, such as overnight. I rely on it while I’m sleeping and it let’s me run a more aggressive basal profile than I otherwise would. When there is IOB, I think the 50% carb intake is a reasonable approach. I’m not disciplined enough to actually do the calculation. I SWAG the amount so I may be higher or lower than 50%, but the same principle applies.

You may not be a superstar at D management but you are a superstar at providing a clear understanding of what to expect of B-IQ. This is very helpful.

May we live long enough for looping systems to achieve what Stockfish and Leela have achieved in chess - being better than even the strongest grandmasters.


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@still_young_at_heart (AKA Maurie):

Thank you! Of course, chess is just the thinking part … But think of autonomous vehicles. When I first heard about it, it seemed impossible … but, now, every time I see an idiot human driver, I think autonomous vehicles can’t get here fast enough. And I spend half the year in Silicon Valley where Wayno and the other “driverless” vehicles are a dime a dozen (still with human “override” in the driver’s seat).

As far as diabetes automation, I fully expect to see commercial dual insulin/glucagon pumps in my lifetime … and I am 70 … likely within the next 5-10 years. (Although I may not live long enough for CMS to approve it for us Medicare types …).

After all, you can have the best furnace and thermostat in the world, but you are still going to be hot in the summer if you don’t add AC.

Stay safe!


It’s already in the works, Beta Bionics iLet. They’ve got an insulin-only pump already in clinical trials and still expected to be commercially available this year. Their dual-hormone system is also nearly ready to go, it was dependent on the formulation of stable liquid glucogon… Which we have now. They say the dual-hormone variant should be out 2022.


Oooh!!! Sooner is better …


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