What would have been helpful to know before switching to Tandem Control IQ?

I have been using the Tandem Tslim original pump for the past five years. I also use Dexcom G6 with the receiver and my smart phone. I have read quite a few posts on this board and other forums that mention different problems people had when switching to the Control IQ. I am wondering what you wish someone had told you prior to your switching to Control IQ?

When I switched from Medtronic Revel 723 I went from a duration of 4 hours to 3-1/2 hrs on Tandem Tslim. Now it will be another switch from my present setting of 3-1/2 hrs to 5 hrs. Sounds frustrating.

Unfortunately, there aren’t a lot of users who have been with Tandem through that first gen and upgraded to the X2, with or without Control-IQ. Hopefully you get some more seasoned answers. They just didn’t have a lot of support from the (Medtronic indoctrinated) medical community in the early days. Also, while I’m a BIG Tandem promoter, first gen products never hit the nail on the head and they had to grow based on user feedback. Overall, if you liked the original t:slim, I think you will LOVE the X2. You should notice fewer annoyances and more intuitive interaction. If you haven’t tried it out yet, I would definitely recommend downloading the t:simulator app from either the play store or apple store so you can familiarize yourself with the changes.

I don’t know a lot about the differences between models, but I think they’re largely just in the user interface, other than the obvious Dexcom integration and subsequent automation.

I’m pretty sure the fill process will be different for you, not a lot, but enough that you should watch the training videos carefully. Like, I think the having to remove the air from the cartridges yourself step will be new to you. Also, you’ll find a lot of the words in the confirmation screens to be replaced with “:x:” and “✓”.

The “time remaining” on your IOB will disappear. Instead it will just show you how much active insulin you should still have working in you. It’s a teeny, tiny change, but one that’s the hardest to get used to because it’s such an ingrained habit.

Also, you can no longer set a specific duration of insulin action. That’s a hard one for people to accept, but the reality is that the model previously used (by all pumps, if I’m not mistaken) didn’t really match up with how people actually use up their insulin. It was just a straight downhill line (linear decay), and people had to screw with the DIA setting to try and force the pump display to match their personal reality. What actually happens to our insulin is a lot more curvy, which is what the new model uses (logarithmic decay). That model looks a lot more like the steep downhill part of a rollercoaster. A gentle curve at the top, then a steep fall, and slowly leveling out to even at the end. Because of that long tail where it’s approaching zero, it simply doesn’t matter much what your previous DIA was. The new algorithm levels the playing field, so it’s hard set at five hours, which would really suit anyone who had like a 3-4.5 hour DIA previously. Note, that’s my personal guess/observation. You won’t find those numbers or explanation on any Tandem material. As an inherently difficult person, the set DIA is my biggest complaint. I have unusually slow insulin absorption. My DIA was set over 5 hours previously. Because of that, I consistently have have hypo incidents 4-5 hours after a large bolus. The pump starts reading zero IOB around the 4 hour mark (the time actually varies depending on the size of your bolus, it could be much sooner with a small bolus), and I personally still have a lot of insulin working at the 4 hour mark. Since I like to use the sleep mode constantly for the lower target BG, the pump will increase my basal if I’m over 120, not knowing I’m still coming down from my earlier bolus. I’m a pain in the butt, though. For most users, you just need to let go of the aggravation that you can’t control the DIA setting.

The only other thing I can really think of that might be off-putting with Control-IQ, is that you can’t set a specific target range anymore. It is hard set at 110,v which is slightly higher than a lot of us want to use. That only really matters if you’re in the habit of using the bolus wizard, though, which I seldom do. I usually quick bolus.
You could always add a little bit to your calculated bolus if you use the wizard and want a lower target.

The positives of Control-IQ FAR outweigh those previous points, though. My A1c is the best I’ve ever had (5.8, and I never had it lower than a 9 in my 30-year history. I thought my doc was going to kiss me, she was so pleased!), and my diabetic life has been sooooooo much easier to boot. I can literally just guess at what I’m eating, and Control-IQ works it’s magic in the background. Again, since I’m a pain in the butt, I have to make a mental note to eat a bedtime snack if I had a high carb dinner, to cover the insulin I know I still have on board, and I give myself a tiny additional bolus (0.05 units) to prevent Control-IQ from raising my basal. It won’t increase insulin for an hour after any bolus. And then I get to sleep through the ENTIRE NIGHT without a single alarm to wake to me!

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My ONLY complaint is that I cannot extend boluses beyond 2 hours. Other than that, I’ve been extremely happy with it. (edit: I also run sleep mode 24/7, unless I’m exercising, and then use that for about 1 hour ahead of time until I’m done working out!)

Allison, what has your average BS been running ?

About 130-150 according to Dexcom. My time in range (range of 75-160) is about 70-80% most weeks.

My current Tslim pump was manufactured after April 15, 2015, so the cartridge fill process requires that I remove air from the cartridge prior to filling it with insulin.

One of my concerns is that the Tslim screen and I am assuming the X2 screen are the same size. Doesn’t this make a lot of information available to the user in a small space? I had cataract surgery the end of January and I’m still experiencing vision changes. I just hope my vision settles so that I can read the small numbers clearly. No one’s problem but mine I guess.

They reorganize the screen when you run the CGM on it. Your current data is very easy to see, and your graph is easy to see… However, I find it difficult to discern an exact number from any data point on the graph history. The graph shows a full range of 0-400 mg/dl all the time, and there are no grid lines. You can’t click on a data point and get a pop-up display of the data, either. I find it a little hard to guess EXACTLY what a glucose was in the past via the pump screen alone.

For instance (note the this is a crappy picture I took of another screen with a crappy camera app that I never get focused well. The real screen is not fuzzy!) :

I had a really odd night, I don’t know what the heck happened. Usually I have very pretty flat lines all night, but for some reason I went high at 6:30 am (didn’t wake up until 8, and I don’t think I was sleep walking and snacking), then went low. This is very unusual. I’ve been traveling for the last 5 days, though. Road tripping to pick up building supplies in Phoenix, and car camping to avoid people. I don’t know if it was simply exhaustion kicking my butt, or an error related to my sensor being nearly a month old and haven’t calibrated it since before I left home and my transmitter being 109 days old and due to die any minute, or what…

Anyway, you can clearly see I was just over 180, but I don’t know exactly how high. I have to look at my cell phone to see that the 3 out of range readings were 183, 187, and 184. Thankfully Control-IQ brought it back down in it’s own. You can also pretty clearly see where my basal was completely suspended to prevent the oncoming low, as indicated by the red stripe, but again I have to check my phone app if I want to know exactly how low I went before it rebounded (63 was the lowest point). You can also pretty clearly see that I haven’t charged my pump in nearly a week. LOL! (I went to bed at 20%, but the vibration from the alerts drained 10% overnight alone) You don’t HAVE to bother knowing what all the other icons mean, they really don’t matter and you can the information clearly spelled out for you by tapping the top corner of the screen around the cartridge gauge. But, the cloud icon means “sleep mode” is engaged, the diamond icon next to it means my basal is still reduced, because I’m under target but no longer completely suspended, that is also indicated by the yellow “B” in the top right corner. The only other unusual symbol is a radio tower next to the battery interdictor showing its getting Bluetooth radio signal from the Dexcom.

See a better commercial picture for how clear/bright the screen really is:

I think it’s key to keep in mind that a lot of D gear gives a false sense of precision by presenting you with a numerical value. This was brought home to me more pointedly during my sojourn with the 670G, and the DIA setting, which was about the only tool the system let you adjust to make automode more or less aggressive. I came to realize it was only notionally about your actual insulin duration and really just a dial for turning the microbolus rate up or down. It certainly bore little relation to what my DIA had been on my pre-670 pump.


Thank you for your post including pictures of the Tandem screen. It is really helpful. It seems like a lot of information on one small screen and I was afraid things would be too small for my viewing.

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You might call your endo and see if they have one that will allow you to see the screen. My endo has a diabetic educator that has samples of all pumps to look at.

Here is good article that explains basal-IQ vs Control-IQ, that I found helpful.

I started X2 last week and details in article on control-IQ were helpful.

I have only been using CGM for maybe 7 years and a pump for about 5. All of that CGM time has been with Dexcom G4, G5, or G6 and pump has been all with Tandem … the original t:Slim, t:Slim X2 (vanilla), and then Basal-IQ upgrade for several months and Control-IQ for the past several months. I have never even seen, much less used, a Medtronics product so, from that perspective, my view of the world is somewhat limited.

I’m not certain why the no longer allow you to set insulin duration … but, for me it has been a non-issue because my original “optimum duration” was set at 4 hours and 45 minutes so moving to 5 hours is a non-issue for me.

Note: I am using “vanilla” Control-IQ. In other words, I haven’t tweaked to be more aggressive by increasing my basal rate, putting in a “funny” number for my weight, or running it in sleep mode around the clock. That said, my TIR has increased from 65-70% to 80-85%, my average glucose is running about 140 mg/dL instead of 150-155 mg/dL and my standard deviation has dropped to about 40 mg/dL from 50-55 mg/dL. I know that lots of you have FAR better numbers than I … even without these new-fangled tools … but for me, at least, this has been a big step forward.

Like @alisonl, I miss NOT being able to extend a bolus beyond two hours. For me, however, that is something I usually only need to do when I eat in a fancy (read high-fat recipes …) restaurant.

I miss not being able to see the “time remaining” along with IOB but expect that because the Control-IQ algorithm is periodically adding boluses and/or tinkering with basal rates, that “time remaining” for the IOB is a tricky thing to determine. How much do I miss that? Not that much …

Note: none of these things were surprises in that they DO tell you these things during the online training … but, by the time you are doing online training, you are pretty far down the upgrade path.

For me, upgrading first to Basal-IQ and then to Control-IQ have been big improvements and I’d hate to go back to the open loop world.

I will certainly look forward to future iterations of Control-IQ as I believe that this is only the first pass at improved closed loop control.

Note: Tandem has recently released their t:Connect app where you can see virtually all of these things that you see on your t:Slim on you phone. At this point, it is not a two-way connection so you can’t control your pump or acknowledge alarms on you phone … but, I have to assume that capability will be added in an upgrade of the t:Slim/t:Connect app. When that becomes available, I expect that using the better accessibility features available on a phone … particularly if you have a big phone … may help with some of the vision issues of trying to read everything directly on the t:Slim screen. There is clearly a lot of information there in not too much area … and most of us likely don’t want to wear a tablet-sized pump.

I hope that you are as happy with Control-IQ as I have been.

Stay safe!


I have t:slim x2 (i beleive). I also use Dexcom g6.
Can someone explain how to go about getting the Basal-IQ and Control-IQ on my pump.

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Login to the Tandem user portal. Go to the “my devices” page and you’ll see your pump, including model and software version. Click on the “upgrade my software” button to get started. That’s what’s on my screen, but I have a pending update I didn’t install yet. It might say something like “check for software updates” instead for you.


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I got it all done in 5 hrs. Just completed the training and update.
I now have the Control-IQ in my pump. Looks like i like the features