Considering T:slim X2 - Question about lows

I’ve been on the 670g system now since April '17 and have had what I consider a good run with it. I am seriously considering switching to the T:slim X2 Control-IQ because I can’t find where the 770g is a major improvement. Plus, the T:slim integrates the Dexcom system.

Prior to going to the 670g (I was exclusively MDI for 20 yrs, 670g is my first pump) I fought night time lows. While my A1C were improved moving to the pump (6.8’s to 6.1’s), the biggest benefit has been the elimination of night time lows. In the past almost 4 years, I’ve not had a single low blood sugar episode at night while on the 670g.

So my question: For those of you on the T:slim X2 Control-IQ, what has been your experience with night time lows? :smiley: EXTRA POINTS FOR THOSE THAT HAVE USED BOTH the 670g and T:slim :smiley:

I have only used the TSlim, but my lows have almost completely been mitigated by CIQ. The last time I went below 65 was a seriously rapidly descending low that even Dexcom had trouble keeping up with. Any other low I have had since migrating to CIQ has been managed by the pump and I almost always come in for a soft landing at 100 and stable even when exercising. I’m a fan. I’m a seriously big fan and don’t see myself changing to a new pump anytime soon, even though my warranty is almost up. When I first got the TSlim I had minor “tubeless” envy. Now, with CIQ I could care less.

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I’m a massive fan of Control-IQ. It’s life changing. The only time I have a low I have to treat is if I didn’t like dinner and didn’t eat anything remotely close to what I bolused for, when I was running a wicked fever (actually needed the glucagon for the first time in 20 years, it was a scary fever!), or intense exercise that wasn’t anticipated (chasing cows that got loose of the fence). And those are daytime lows… Nighttime lows are 100% completely eradicated (excluding something like that crazy fever), because of the “sleep” activity setting. The pump will flatline you somewhere between 110-120, unless you tweak your settings to target a lower value.

The pump doesn’t wake you up at night with Control-IQ.

That said, you’re completely in control of how it behaves, because it adjusts insulin according to the settings you enter. It’s not trying to figure you out like Medtronic’s system. So your success with it depends entirely on your ability to understand and correct/adjust settings…or at the very least having a capable medical team to help you do so. If you program a correction factor (ISF on Medtronic) that is too high, it will cripple the pump’s ability to adjust your basal. You’ll be stuck in whatever direction you’re heading, whether that be low or high. The pump generally behaves happiest with a lower correction factor than expected, but if you set one TOO low, Control-IQ will over-correct on both ends of the spectrum, resulting in both highs and lows before it changes direction.

You can expect to have to adjust your settings coming from Medtronic. Because of differences in delivery, absorption, and accuracy, your insulin needs will most likely be different. Because of this, you will probably dislike Control-IQ right out of the box. But opinions unanimously change once the settings are tweaked and people fall in love with Control-IQ.

I didn’t earn your bonus points, so I’m summarizing what I’ve seen in the Facebook groups… Which you’re welcome to join yourself. The “are you happy you switched?” question is asked several times a week. T:slim X2 was my first pump, and I loved it for 2.5 years before Control-IQ was evev introduced. Now that I have Control-IQ, I can’t imagine giving it up. I actually joined a 780G Facebook group, because my own warranty is expiring this summer and it’s time to start re-evaluating the options. The 780 looks like a vast improvement over the 670, but it doesn’t seem nearly as impressive as Control-IQ.


Thank you El_Ver. Ok on the “tubeless” envy :slight_smile:
I’ll admit, and its mostly vanity speaking, I don’t like the the way the T:lock looks. Then again, I didn’t like the little bit of tubing hanging out w/the Medtronic pump either, and quickly got over that.

Thank you @Robyn_H

Exactly the kind of feedback I’m looking for, so consider your extra points reinstated.

I did not realize there was “control” of the Control-IQ process. That’s good to know. In general, i have no complaints about the way the 670g performs overall, but it’s very “locked down” and while I’m certainly considering the 770/780, there is so little information about what’s actually new and improved other than bluetooth (i could care less).

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The 670 and 770 are functional equivalents with the major difference of using share. The 770 has remote update which will allow the implementation of the 780 software. It will also allow setting the preferred blood sugar at 100 instead of 120.

I have also noticed the number of alarms in the 770 to be less than 670. I really like the 770 and have even better hope for the 780.

Note: I am a Medtronic ambassador. My opinions are my own. They did not pay me to say nice things. OK, they sent me a shirt and a cup but even I am more expensive than that.

The T slim X2 with Control IQ is my first pump but it has made my life easier and nighttime lows are fewer and less disruptive. Before dexcom however nighttime was the most dangerous time for me with lows. Where it really shines for me is dawn phenomenon though. I used to wake up to annoying swings in BG in the early hours of the morning and now I am reliably in the 90’s to low 100’s.

I just started using the Tandem T:Slim and once I got the settings right I haven’t had a morning reading higher than 112. I’m a big fan of the control it gives me compared with MDI. I would recommend buying the holder with the plastic “cell phone” clip. The metal clip it comes with doesn’t hold up to daily use.

I’m a fan of the T-slim. It definitely helps a lot with overnight control on both ends – not going too high, keeping from going too low.
For what it’s worth, though, I can’t come near matching your four year streak, but, as Robyn explained in her post, that could be because my settings aren’t fine-tuned enough. I’d be interested to learn more about how to do that. I just kind of let my settings be and they seem good enough.

In terms of what Control-IQ can do. The other night I went to bed with a BG of around 87. Control-IQ kept my basal off for a couple hours while I slept and my BG hovered in the 80s. When my BG finally started going up, the basal kicked back in and it kept it around 110-120 all night. Before Control-IQ I would never have gone to sleep with a BG in the 80s without eating something so I thought that was pretty nifty.

l have had maybe five or ten lows that needed to be treated at night over the course of the last year…nothing like your four-year streak, but I’m sure I bear most of the responsibility for that…Some of them might have happened because I corrected in addition to Control-IQ correcting. None of those lows were severe (below 50, say).

I just downloaded Tandem’s t-connect app to my phone and I think it’s great. It shows you right away when and how much of a correction Control-IQ has given you. This information was always available on the pump (by looking in “History” or keeping an eye on your IOB) but with the app it’s just so much more immediately visible. I’d highly recommend the app.


This is a double edged sword in my opinion.
I do t sweat lows or trending lows anymore because I figure my pump will correct it.
I can go to bed with a 75 and not worry at all. I can’t remember last time I went under the 55 alarm.
I pretty much alway wake up in the mid 90s. I draw a pretty flat line all night even with a pretty intense predawn phenomenon.

In reality I should not go to bed with a 75 but I’ve gotten to the point that I trust the technology.

It’s like driving a Tesla in auto mode while watching a movie.
It works great 99 percent of the time, but there is some risk when you stop paying attention to it.


Night time lows and waking up being 250 all night long are gone.

Highly recommend.

Wait what? You are waking up at 250? You might need an adjustment.


Thank you for confirming that @Rphil2

Today I came back into house, after shoveling in 15 degree weather, with pump in shirt pocket, under layers of coats.

Came back in 40 min later to find NO CGM reading on my pump or phone. Sensor is on inner thigh. Error message said CGM unavailable alert 39.

Reset phone, Bluetooth and at first no luck. Just about to call Tandem, and cgm reading started working again.

My guess is that my sensor/transmitter temperatures got too cold, and unable to respond to send reading. Just a heads up to others in this winter wonderland!!

But also to warn that when pump loses cgm data, it defaults back to profile. In my case, I felt going low and treated while still outside.

The sort of disconnect you describe is more or less what I’ve come to consider typical of my experience with the t:slim x2 & G6.

My preference is to wear the G6 on my outer upper arm. My pump is usually on the waistband of whatever I’m wearing on the same side as the arm the G6 is on.

While I am in bed if I pull my G6 arm out from under the covers and put it around the cat snuggling up against my side then the pump & G6 are likely to lose their connection. In other words, the signal can’t make it through/around my arm, the cat’s body, and the bed covers to connect with the pump.

Back when I was still using Medtronic CGM, I would envy those lucky G4/G5 users who seemed to maintain connections from one room to another. Whatever changes Dexcom has made to the G6, that sort of connectivity seems to have been lost.

What annoys me is that while I’m getting connectivity roughly equivalent to the Medtronic CGM, I now lose CGM data as a result of a disconnect. I was rarely aware of when Medtronic’s CGM may have disconnected because, as soon as it reconnected, any “missed” CGM data was transmitted to the pump from the transmitter’s (8 hour) buffer.

Supposedly the G6 has (at least) a 3 hour buffer. However, my t:slim x2 pump does not recover untransmitted data from the transmitter’s buffer. Instead, the pump always picks up with the current CGM reading whenever it happens to eventually reconnect. Implicit in this is that the directional “trend” arrow is lost until the pump gets at least three readings from the transmitter.

I can speculate on what good (to them) reasons Tandem may have had to ignore the data in the G6 buffer. But I personally find it annoying as heck. :confounded:

This cgm “disconnect” gave a different error message (CGM unavailable"), which is why I suspect it was due to cold temp (for sensor/trans). I get the situation you describe, and it quickly self corrects, gives message Out of Range.

So main point is that if out in COLD weather, take note of placement of sensor/transmitter.

This doesn’t happen to me. If I lose connection to the Dexcom for some reason whether pump can’t receive info through my body or just being too far away as can sometimes happen with my phone, the data updates as soon as the next reading comes through.

This sounds like a glitch and I would try calling tech support. They may not have an answer for you but it’s worth a shot. I used to lose data that was supposed to be transmitted to Dexcom’s Clarity app and I did call Dexcom to see if it could be fixed. They weren’t able to fix my issue but when the next update for Clarity and the Dexcom app came out I stopped losing data so someone must of gotten the word out.

What version of the Tandem pump are you using? I have a t:slim x2 with software version “Moonlight v7.4”.

The partial screenshot below is from the upper right hand corner of the dashboard tab of my Tandem tconnect data page. I picked the custom dates (Jan 8 - Feb 15, 2021) to include only three ~2+ hour warm-up periods.

So, subtracting the ~6+ hours when CGM was inactive while it was warming up, I’ve apparently had 4 hours of disconnect. Not the end of the world, but it’s also not how I expected the Dexcom CGM to work. And, as I said, I have seen from the gaps in the CGM graph on the t:connect app on my Android phone that the CGM data during these disconnects is lost. :confused:

CGM Inactive Screenshot 2021-02-16png
Footnotes copied from tconnect page for the data above.

  1. CGM Inactive due to loss of signal, sensor errors or sensor session is not active. When CGM Inactive and Pump Inactive or Control-IQ Set to Off occur at the same time, that time will only display in the Pump Inactive or Control-IQ Set to Off metric.
  2. Pump Inactive due to cartridge change, manual suspension or alarm suspension.

I agree for the out of range message, but not this new message I got. I called tandem and they said to put new sensor in, a replacement would be sent.

However they could not explain difference between message Out of range vs CGM unavailable.