Tslim Control-IQ Help - Sleep Lows!

Hi everyone - I just got my Tslim pump this week and started on Control IQ. So far, the day-time numbers have been AMAZING and my exercise numbers have been AWESOME - I’m so glad I got the pump! However, I’m really struggling at night in “Sleep Mode” and crashing with lows 2-3 times per night. So far, I’ve had to shut off Sleep Mode every night.

I’ve read through the manual (that was a LONG read :heart_eyes: but worth it) and also past posts here, in JDRF and Reddit, but not seeing the answer yet so hoping someone here can share experience.

Here’s where I’m at right now:

  1. The Tandem trainer had told me to set up only ONE profile in the pump with no segments. So I’ve got my basal rate set at .6 and my ISF set at 1:100 all day long

  2. I’m on a very low carb diet so my TDD is averaging 18-22 units day.

  3. I’ve got Sleep Mode scheduled to run from 8pm-8am. But I’m crashing hard at night (getting below 60 every night from 1-2am and again at 4-5 am).

  4. I thought Control IQ was supposed to adjust basal to prevent lows way before they happen so not sure what’s going on here. I do see that the pump shuts off the basal for around 2 hours around those times…but I’m still crashing and the alarms are going off so I’m just shutting Sleep Mode off when the alarms wake me up.


  1. Let’s say I adjust my existing Personal Profile and so that daytime segment basal rate of .6 and then add a new night-time basal segment of (for example) .50 - does adjusting the night time basal rate help? To elaborate…

**What I’m confused about is: does changing the BASAL rate in my Personal Profile for night-time matter at all if I’m in “Sleep Mode” in Control IQ? In other words, does the Sleep Mode OVERRIDE the Personal Profile night-time basal setting and just (for lack of a better phrase) “do what it wants” to get me into that Sleep Mode range of 112.5-120?

  1. Am I perhaps turning on Sleep Mode TOO EARLY? I sleep from 10-6, so trainer advised 8am-8pm. I’m wondering if Control IQ is giving me too much too soon. When I look at t-connect, I can see that it’s upping the basal to get me into range of 112.5-120… and then I promptly crash 5 hours later. Again, is this related to the basal rate set in my personal profile, or solely due to the Sleep Mode range?

Sorry if this is obvious to everyone :grimacing: but I don’t quite understand how it works. Thanks much for any help!

Although I have no Control-IQ or any Tandem experience, I think your instinct about too high a basal rate is reasonable. As someone who has lived with another automated insulin dosing system for four years, I have some questions.

Have you verified any of these lows with a fingerstick? How long does your BG go low during these overnight hypos? Do you treat it or do you sleep through it?

If you treat with some carbs, what do you treat it with? Does the hypo respond to a single treatment or does it resist and make you treat again? If treated does the CGM line rebound into the hyper range, say above 140 mg/dL?

Can you upload a CGM trace of a typical night when this happens? It’d also be useful to see what the C-IQ modified basal rate is doing on that typical overnight, in other words the actual basal profile including the time when it zero-temps the basal.

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We need a little more info. We need to know what was going on before the low, how bad is the low, and what exactly Control-IQ did.

What do you mean by “Tandem trainer” telling you no timed segments? Tandem has no such policy, and a Tandem employee shouldn’t be telling you dosage decisions. If it really was a Tandem employee, they over-stepped a line, and you really shouldn’t heed that advise. The ability to set different basal profiles is mostly the entire reason for getting a pump in the first place, instead of just taking a long-acting insulin. If this was a CDE who works with your endo, though, that’s a different scenario. In that case, I assume they meant “let’s see how just one basal setting works for you, and we’ll make adjustments later…” Quests what? It’s time to make those adjustments. Your current settings aren’t working for you.

Personally, I find correction factor is the single most important setting to all of Control-IQ. Control. This is the setting that helps Control-IQ predict where you BG is trending in the next 30 minutes and how much insulin it needs to adjust to bring it back in range. If that number is off, things go haywire. You may need to adjust your basal, too, that’s not really my call… But you definitely need a different correction factor at night.


I forgot to add, yes, basal setting really does matter to the Control-IQ algorithm and works in tandem with your correction factor. If your basal rate is too high, and your correction factor is set right, it won’t withhold enough insulin, and you’ll find yourself stuck holding low. Think, if you need to come up 50 pts and your I:c is set at 1:100, the pump knows it needs to withhold 0.5 units of insulin to correct. It uses the basal rate to determine how much time is equal to 1 unit. In your case, that works out to 50 minutes of suspended insulin, during which your liver is supplying uncanceled glycogen to raise your BG. But let’s suppose your basal rate is set too high (which would drive you low in the first place), and suppose your body accrually needs 0.5u/h to neutralize your liver’s output. In that case the pump should suspend insulin for an entire hour to correct, but your pump doesn’t know it’s programmed wrong, so it still suspends for just the 50 minutes, leaving you below target.

All this was supposing your correction was set accurately. If it’s WRONG, it adds a whole nother crazy dynamic to how Control-IQ might misbehave.

Of course, in the real world, nothing is this fixed The pump is re-running the math every few minuteS based on the new Dexcom predictions for where you’ll be in 30 minutes

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@Terry4 Thanks much for responding! I always appreciate your insights in this forum!

“Have you verified any of these lows with a fingerstick? How long does your BG go low during these overnight hypos? Do you treat it or do you sleep through it?”

Yes, I’ve verified the lows with fingerstick. Yes, I do treat it - usually with 4 glucose tabs. If the alarm continues to go off again after 20 mins, then I treat low again with another 4 tabs. I have been going low around 1am then go low again around 4am. My blood sugars are nice and steady at dinner (which is around 5pm) - I’m not eating any carbs at dinner so don’t usually bolus - usually my blood sugar rises a bit as I’m only eating protein. Granted, this is only after a few days being on the pump so I’m sure the data will be more robust and telling after a full week :slight_smile: Thanks for chiming in on your thoughts on the basal rate - much appreciated!

@Robyn_H Thanks for your insights here, much appreciated!

Re: the Trainer - yes to the latter :slight_smile: CDE Trainer was working with Endo - after reading your post, I’m sure she must have meant “let’s keep it simple at first with just the one profile and make adjustments later” - but I had interpreted it as “you only need one profile” (that’s why I was wondering if Control IQ perhaps overrides the Personal Profile settings).

Thanks much for your thoughts on the correction factor and Control-IQ - super helpful! I had forgotten that one could have/needed to have a different correction factor at night! I’ve been on MDI with Tresiba + Humalog for 5 years and for some reason I thought the correction factor just stayed the same all the time. I’ll need to go back and look at my old Animas ping settings and see what I used to do just for ISF at night to get some more data. I’ll also go back and read my old “Pumping Insulin” book on how to test the overnight correction factor. Thanks for that last paragraph too on the basal. Very helpful!

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I also started tandem X2 recently, and started with 24 hour sleep. But had some times going too high, some too low overnight.
So I did sleep mode only overnight and tweaked my settings to get overnight right. Then played with other settings to improve daytime. Once that was working, I tried sleep 24 hours and so far it’s working well, improving over my initial time with 24 hours sleep. Both basal and sensitivity were tweaked.

I try to change one thing at a time, then wait a few days for next change.


@MM1 - Thank you for chiming in! Are you using Sleep Mode for 24 hours because of the tighter range (112.5-120) of control? I appreciate your note about tweaking one thing at a time :heart_eyes: That’s a good reminder as there are so many things at play. I’ll probably start with adding a segment to my Profile for evening and tweaking the basal first. Thanks again!

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Yes. But also am willing to pay attention and make adjustments for daytime oddities related to using sleep all day.

Another thing that I think was throwing it off for me is my habit of several mini meals/snacks during day. If I used bolus wizard and enter carbs, and there was IOB, it would reduce dose for those new carbs. But that IOB was still needed for prior carbs/proteins still impacting BG.
And I don’t enter bg for calculator, because I know if I have already corrected for it, usually with a .5 quick bolus. These are habits I had during 25 years on medtronic pumps, and no reason to change.

If you’re eating a carb-limited diet, then you may need to bolus for the protein content of a meal. This will require you to experiment some but a formula that I’ve used successfully in the past is to count 50% of the protein grams as “carb-equivalent” grams.

What worked for me was to use a pump-extended bolus to cover that protein. For a high protein meal containing meat, my bolus would extend out over three hours or more. You’ll need to experiment to find what works for you. To be safer, you may want to experiment with a meal earlier in the day so that you can actively watch what’s going on while you’re awake.

If you need to eat four glucose tabs at 1:00 a.m. and then another four at 4:00 a.m., that suggests you are infusing too much insulin overnight. Insulin can be reduced by decreasing your programmed pump basal rate or making your insulin sensitivity factor less aggressive like going from 1:100 to 1:110. Changing a little bit of each of these settings may be what’s needed. Again, personal experimentation can inform your choices.

What insulin are you pumping and what insulin duration did you program into your pump? If insulin duration is set too short then that can also lead to over-infusion.

You need to consider all your personal factors to make a decision on what, if anything, needs changing. It could be that an aggressive exercise session the day before might be increasing your actual insulin sensitivity.

Do you have access to a CDE? It seems like your circumstance as a new C-IQ and pump user justifies some specific advice from a Tandem-savvy medical professional. Someone like Jennifer Smith at Integrated Diabetes comes to mind. She’s a long term T1D and a CDE available for remote counseling.

By the way, don’t think that you are on a quest to identify the perfect pump settings that will lead to great control. As I’m sure you’re aware, diabetes is a moving target and this new diabetes-tech does not change that. The better you understand your fundamental settings, the better you’ll do!

@Jolene7 Terry gives incredible advise, but I need to interject here and beg you to please be careful with Control-IQ and this particular piece of advice. This recommendation to raise the correction factor is only valid if it were control-iq driving you low in the first place. Did you have readings over 120 before you went low? If it’s the high basal driving you low, raising the correction factor will actually decrease the pump’s ability to get you out of that hole.

When your correction factor is too low, changes happen violently and quickly. Control-IQ will over-correct for any number higher than your target upper limit (120 in sleep mode, 160 in exercise mode, 180 in default), then send you crashing low, suspends too much insulin… Just to see you overshoot your target again, and start the cycle all over.

When your correction factor is too high, all your automatic corrections move at a turtles’s pace, but will ultimately get you to a flat line. If you’re suck high and get down or stuck low and can’t get back up, it’s good indication your correction factor is too high.

You’re looking for a magical number in between, which surprisingly enough may not look like anything you’ve used before.

If I had to wager a guess, with the disclaimer that I’m not a medical professional… just a biology/technology geek, I would only agree with half of what Terry said there. Personally, I think you need to both reduce your basal AND reduce your correction factor at night.

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Same thing happened to me when I started Control IQ. I only tolerated that for one night before dropping my overnight basals and it resolved the problem. The basal rate that I was originally given by my Dr. works perfectly for the daytime but is way too high at night. My Tandem trainer recommended that I start sleep mode WHEN I normally go to sleep and end it when I normally get up and that has worked well for me.

I am still having minor issues like going higher than I would like after meals(which is keeping my SD high) but overall going pretty well and eating what I want (within reason).

BTW, @Terry4 Control IQ has a set duration for IOB of 5 hours.


If you are high after meals then you just need to adjust your carb ratio. If you are high generally then you should lower your sensitivity.
I lowered my sensitivity so I could stay lower when fasting and at night and it is also much more reactive for meals.

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@Jolene7, Now that you are getting the minor adjustments into your plan, there is one other gremlin you should research and plan for its occurrence.

The new gremlin you may encounter is “COMPRESSION LOWS” showing up on your CGM, awakening you in the middle of your slumber. Simply, if you deep sleep on your CGM sensor/transmitter in the middle of the night, you mash the tissue so the fluid around the sensor wire does not get fresh fluid with ‘sugar’ and the cells around the sensor wire ‘eat’ the sugar without replacement and the sensor reports a LOW.

Welcome, stay in learning mode. Share what you learn, it helps us all learn more.

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Thanks to everyone who responded!

Basal: I adjusted my overnight basal and changed it from .60 to .525 and it worked perfectly - I finally got a full night’s sleep yay!


@Terry4 and @Robyn_H - Thank you both so much! For ISF, I read both of your posts several times and I finally realized that I’m getting confused by the language :slight_smile: and how it actually applies to the numbers and the “math” - words like "aggressive", “increase” “decrease” and “high” …hoping you can clarify:

@Terry4 - when you said “make your insulin sensitivity factor less aggressive like going from 1:100 to 1:110” I think this was similar to when my CDE had said " 1:85 is more aggressive than 1:100" but I just want to be sure what you’re saying. You’re saying that increasing the denominator is LESS aggressive, correct?

@Robyn_H when you said "I think you need to both reduce your basal AND reduce your correction factor at night" - For ISF and “reduce,” does that mean the same thing Terry said above? E.g. is changing the setting from 1:100 to 1:110 the same as reducing the correction factor?

Also, when you said “when your correction factor is too high does HIGH refer to the denominator? E.g. is a correction factor of 1:100 HIGHER than a correction factor of 1:110?

I’m sorry :grimacing: I’m getting very confused so I just want to be sure I’m understanding what you’re both saying. Thank you!

@Firenza Glad to hear of someone with a similar experience :heart_eyes: thanks! I really appreciated your comment on starting/stopping sleep mode manually. I’ll try that tonight!

PS - I found this great overview and it’s helped with the overall settings

@Terry4 - PS - Yes, I still have access to my CDE and thanks so much for the name of the other CDE you provided! I’m definitely in touch with my doctor and CDE - both of whom I have great respect for … but they don’t actually live with type 1 on a day to day basis. I’ve been reading this forum for years, so in addition to the input from my doctor and CDE, I also really wanted to hear from my peeps - all the amazing folks here who deal with the “reality” of type 1 every day in real life :heart_eyes:

It’s a challenge to convey with words the meaning of mathematical inverse relationships, the nature of the insulin sensitivity factor or ISF.

I deliberately avoided using the terms “increase or decrease” to describe changing ISF since it can confuse. If one increases the ISF from 1:50 to 1:100, it means delivering less insulin to correct a high blood sugar. Conversely, if you decrease the ISF from 1:100 to 1:50, you will deliver more insulin.

This inverse relationship between the ISF and the amount of insulin it ultimately delivers is a semantic challenge. I tried to use the terms “more aggressive” or “less aggressive” as it makes a connection between more or less insulin delivered.

In math, things can vary directly or inversely. People can intuitively grasp direct relationships more easily but the inverse relationship can confuse.

If you share a pie with more people then the size of your slice will get smaller. Therefore, the number of people you share your pie with varies inversely with the size of your slice.

Have I further muddled this or do you catch my meaning?


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What those of us who love to share what we’ve learned with others on an earlier phase of the journey struggle with is avoiding coming off as definitive. We are not doctors, but you obviously grasp that.

I would rather not have to do that dance since I believe that the basis of my knowledge is different, yet extensive and compares well with the basis of a doctor’s knowledge. What I know, however, differs qualitatively from a doctor.

In a forum like this, we need to somehow make that clear so as not to mislead. I just wish doctors and other medical professionals would reciprocate in this . I’ve yet to hear one of them disclaim, “While I’ve never lived with diabetes, here’s what I would do.”

They should acknowledge that there exists a huge body of knowledge representing the lived experience of diabetes. And that this lived experience is valid and valuable. Their scientific and clinical knowledge base does have its limits and sometimes the diabetes lived experience is more pertinent – a point you get but others may not.

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At the end of my last visit, my CDE of 15 years said, “But remember, I don’t LIVE with diabetes.” I thought that comment was remarkably intuitive. BTW, she has always had a problem with the inverse relationship of the ISF and I have had to correct her. I found that she doesn’t accept corrections well. None of the health professionals seem to. :astonished:


Actually, no. I was disagreeing with Terry on the correction factor change. I’m sure the different wording doesn’t help things much, correction factor vs sensitively factor. I was speaking about the actual number, not how it affects you. Making small changes, though. Like say try 1:97, instead of 1:100.

Yes, the smaller number is more aggressive, but it works both ways. It will get you out of the hypo low faster and hopefully work at avoiding lows better. But if you overshoot the mark with TOO small of a number, it will actually cause hypos when doing a correction… In which case Terry’s advice to go from 1:100 to 1:110 (though I think that’s too big of a change to make at once) would be true. BUT, it’s only good advice if you were high first. That’s why the very first thing I said was that we needed more info about what was going on before the hypos. You said enough to leave me with the impression your basal rate being too high was the biggest problem… But Control-IQ could have handled those hypos better if your correction factor was reduced to, say, 1:97.

You’ve got to keep trial and erroring until you get the correction factor dialed in. You might very well wind up at something unexpected, like 1:75. But overall, small changes seem to make a big difference. I would never make a change more than 3 mg/dl at a time. Try it for a few days before you decide to move it farther along. If you ever reach a point where you’re actually seeing more hypos, over-shooting the 110 target on the rebound, and when you look at your statistics you notice your GVI (literally a measure of how flat your trend line is) getting bigger… Then you’ll know you pushed your correction factor too low.