Tandem pump pro tips?

Hello everyone. I’ve been on the Medtronic pump for about 10 years but I just switched to the Tandem + Dexcom combo and I really like it. Can any of you give me some advanced tips or “off-label” tricks?
For example, can I just change the site and not the cartridge? Do you ever reuse a cartridge or the filling syringe?
My phone is not on the very short compatibility list for remote bolus, is there any way around this with a 3rd party app or something?
Can you tweak the settings to get a lower BG target to improve control? Or do you just get creative with the basal rates or something?
I come from a background of managing it all myself and using 3rd party or homemade apps and even hardware is not a concern for me. Or is there another site where people like me talk about this stuff? Thanks

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There is nothing in the guide or clinical data that says you cannot fill the cartridge up and continue to use it through multiple sites, only disconnect at the site, never at the pump end of the line. Be sure to leave the old site in, fill the cannula and prime the new site. Don’t reuse cartridge or syringe.

Keep looking at the mobile bolus compatability list for updates. There is a build your own app for Android to operate the Tandem.

Basal testing is cretucal to get the settings on the mark. Do the testing with CIQ off or running in Sleep mode. There will be multiple rates at different times of the day. Then work on ISF/CF and I:C ratios. With ISF the lower the number the more aggressive corrections, using auto bolus or basal rate adjustments with CIQ. I.E. 1:20 is more aggressive than 1:30.

Tighter control is possible using Sleep mode and doing you own corrections. The carb data you use in the bolus screen is not used in the algorithm, just in the calculation math.

Lyumjev works great with CIQ, Tandem is doing clinical testing now to get the data to ok it for theT:Slim.


Thanks, very helpful.
Curious why you say don’t reuse cartridges. I did it all the time on Medtronic. Is there something really different about these ones?

Do you have a link or a name of that android app you mentioned?

Good idea on the sleep mode, I’ll check that out.

There is an increased chance if introducing contaminates and air into a reused cartridge, it’s made differently than the syringe used in the Medtronic. The pumping is different and the insulin is in a plastic bag.

To get the name o the app go to the FB groups for Tandem.

Note that nothing is more important than basal rates being on the mark with CIQ.

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Thanks @Sjwprod for all that useful information.

Regarding reusing the cartridge, there is no mechanical barrier to doing that from the tandem side - you can take an old cartridge out and refill it and put it back in and the pump will accept that. Clinically it might not be the best thing to do, but you can certainly do it.

I am a very non-technical user of the Tandem CIQ, and I would agree with @Sjwprod that getting the basal rate right is key.

I think that the intent of “semi-automatic” systems like CIQ is to take on the burden of insulin management with only the most obvious inputs from the patient (like bolusing for food). In that aspect, CIQ is quite remarkable.

I am sure there are lots of hacks with different activities etc that you can do to give you better control.

Let us know what you find - it’s always interesting to hear about different approaches and their results.

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Very helpful, thanks.

Here’s the difference. With the Medtronic reservoir, the plunger travels the length of the reservoir one round trip to deliver 300u. In the Tandem cartridge, there’s a small horizontal shuttle/plunger that rattles back and forth about a zillion times to deliver 300u.

I’ve refilled Tandem cartridges. The second fill of 300u seemed to work ok. The third fill of 300u maybe wasn’t quite so good. I got a sense that I was getting a little bit underdosed, moreso towards the end of that use. The story I told myself was the the seals on that little shuttle plunger were wearing out and leaking, so not as much insulin was pushed out as the pump thought. We can call it a rumor, not a fact.

Since a cartridge lasts me 5 to 6 days, and since my insurance is reasonable, I feel like I get good use out of a cartridge with just a single fill. The great bulk of the cost of supplies is in the infusion sets; I change them every 3 days to help avoid scarring. But if I were under severe financial pressure, maybe I’d reuse a cartridge for a second fill.


Interesting. Is there a picture or diagram somewhere of how the cartridge works?

How about the photo in the reply that is immediately below your initial question? The horizontal area below the green check mark shows the pump shuttle.

If you mean a diagram with explanations, maybe there’s something in the Tandem patent filing, but I haven’t looked for it.

It actually functions like a hand billge pump so that it can deliver a specific amount of insulin and load a specific amount of insulin with each movement. It’s slower but more accurate and not impacted by the environment or conditions.


Interesting. Thanks.

Here is a video on cartridge delivery.


I don’t normally reuse a cartridge but I have occasionally done so. Most of my reuse cases are when a full infusion site and cartridge change is inconvenient (like in the middle of the night). The t:slim X2 cartridges need at least 120u (1.2ml) of insulin and you always have to purge the line (a minimum of 10.2u) even if it doesn’t need it. I keep the previous cartridge and the previous syringe just in case I have a failure with the next set. I’ve actually had more syringe failures (plugged needles) than I have cartridge failures.

I run 100% in sleep mode because it has a lower target range. My exercise consists of daily 20-40 minute walks with the dog and I don’t use activity mode.

My insulin needs are pretty high and with U-100 Humalog, I only get around 2.5 days per cartridge. I don’t really understand how I can put 300+ units in, waste the 13u of purging and get less than 240u out of each cartridge. I have switched to U-200 Humalog and that gives me a more reasonable 5 days worth of usage from each cartridge and infusion set.

The original reason for switching from U-100 to U-200 was that my nighttime basal requirements were being limited by the pump. I needed 3.6u/hr but the pump maxes out at 3.0u/hr. I believe this is a bug in the software but with U-200 I tell it I need 1.8u/hr at night and the pump delivers it without issue.


I’m T1 w t-slim pump x 4+ yr. My understanding is that CQI aims for BG of 110 & that can’t be changed. That doesn’t work for me. So I’m not using it. When I’m able to better control what I eat & when they allow us to set our own target then maybe I will.
I used to use a full cartridge til it needed a new one… ~10 days. For some reason, the insulin doesn’t seem to be effective that long anymore, so I’m changing cartridge & insulin (I put in 150u) every 4 d now. Seems to waste insulin, but I haven’t figured out a better way yet.
You can set separate basals for your choice of time periods. The temporary rate under activity menu can be adjusted at will above or below basal rate based on percentage… wonderfully helpful!!
If I’m heading low often just 15 min at 0% fixes it… just need to watch that bg doesn’t rise too far after that!!! Your experience may differ!!
One of my docs would like me in sleep mode 24 hr… but my eating at this time is not conducive to that… maybe yours is … but 110 seems too high a baseline…. Works for others though!!
When changing infusion set, I disconnect at both ends…… overall I love the pump!!
Good luck!!

Just because it sets it’s goal as 110 doesn’t mean you can’t get it to run at a lower number.
I use a fair amount of insulin (fairly resistant.)
But I can easily get the Control-IQ to maintain me in the 90s or maybe low 100s. And I don’t eat the greatest at times.
If I eat a LOW carb diet, I rarely even bolus for food!!!
It’s about playing with your basals and settings to make it work for YOU.
Trust me, it is very doable.
And yes, I always run in Sleep mode. It works far better for me!

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Sounds wonderful! I haven’t figured out how. Suggestions?

More than happy to help.
I suggest doing a little reading on some posts that have been made about this topic. Many mentions of people making edits to their profiles to tweak the settings for Control-IQ to really shine.

Here is a quote, from me, from a couple years ago.

If you are good at figuring out what your dose should be, and not relying on the pump to calculate it, adjust the carb ratio to be a bit more aggressive, and the correction factor to be a LOT more aggressive. This, and having a more aggressive basal, makes it easier for the pump to raise the basal enough to keep the big spikes from happening, and to bring them down in a mild manner.
I put in some intense time at first to really tweak the settings to make it work for me.

BTW, if you are not in sleep mode, the autobolus is only 60% of what it thinks the bolus should be. So even though it boluses for over 160 and rising, it is not enough.
It does a good job of assisting when you forget to bolus, don’t come close to guessing the carbs, or just life! that is still a good thing, but it does wait until you are already climbing higher. By the time it gives the partial bolus, you will be going fairly high, no matter what.
Doing the sleep mode will start giving a higher basal at a MUCH lower (120) BG count, and starts to gain the upper hand before it gets too far out of hand. Thing is, they limit how aggressive it can be, so adjusting the settings to be more than you would normally be at, is one of the only way that we can currently tweak the system to work for us.

As always, adjust these settings slowly.
I like to make an adjustment, then run it for two weeks and watch my overall patterns. I never adjust for one or two days. Two weeks is my shortest time frame that I adjust pump settings for.

Also, create mutliple profiles on the pump! You can copy what you have and make adjustments to that. Keep the current profile there and safe. Very easy to switch back to.
I had three profiles while testing. Now I am back to just two (one for Novolog, the other for Fiasp/LoomJev).


Thank you! I’ll have a look!
I’m not totally off base (my GMI is 6.0), but making adjustments is not intuitive to me. One of my docs would like it at 5.2. :slight_smile: So would I … I need to make mindset adjustments along with pump adjustments :slight_smile:

Thank you,

Thank you again!
I have turned on Ctrl IQ…
(I’ve been ‘fighting’ a cold & dragging a bit. )
Thank you for the above heading, I hadn’t found a subgroup that seemed to apply!!
Been reading & rereading your enclosed post (seems most applicable!)
So you don’t have any problem w Fiasp in your pump? (Others seem to.) I often use it by injection for corrections, but the pump could give finer tuned corrections :slight_smile: I still have NovoLog in my pump… & in my refrig. Will use it up.
It was seeming that after 4 days the NL in my pump wasn’t as effective, so I’ve been only filling it half way, & changing it every 4 d :(. (infusion sets every 2d).
(It takes 4 d for the pump to really figure out how much is in it. Wish it could figure it out sooner.)
I appreciate your comment about needing to be more aggressive. I had somewhat adjusted based on a YouTube I had seen, but I’ll keep working on that.
And TY for suggesting multiple profiles as I tweak!
Tweak 1 started :slight_smile:
Thank you!

Because of the way the Tandem pump moves insulin Fiasp may cause some clogging. Lyumjev works great in the pump.

Open a new vial, Novolog should be fine for at least 6 days.

After delivering 10u the display should display the amount correctly. If there is a + next to the number it’s still working on the measure.

Aggressiveness with the settings is a big mistake. If you need to be more aggressor get the numbers you want try sleep mode 24/7. Aggressive settings indicate that your basal setting are most likely off. Basal rates being on the mark are key to having CIQ work best. This is a quite common error with using the pump. A CF that’s too aggressive will have the basal and the CF fighting constantly with a roller coaster ride as a result.

Do basal testing, and check it every once in a while. Don’t do basal testing with auto bolus enabled in normal mode. BTW, auto bolus will only deliver 60% of the correction dose every hour, so it’s not designed to counter missed doses or basal rates off the mark. Your body’s basal needs will always vary throughout the day, don’t be taken aback if night sleep basal needs are much different than the daytime, that’s normal and often not understood.

Key to setting CIQ is patience and don’t force setting to work, like being overly aggressive, this causes nothing to work a it can.