Tandem Tslim Pump Cartridges

Hello: I have recently switched from my Animas Ping to a Tandem Tslim. There is a lot to like about the pump but I have a few questions for current Tandem users.

For one, I have noticed that it seems to waste more insulin than my previous pump. When I fill a cartridge I am using a syringe with 150 units. However, several times my pump will give me a reading of about 80 or 85 units. I realize that I have to account for the priming (13.5 units for my contact detach true steel infusion set), plus the pump does not give a number until you have used 10 units and yes, there is supposedly about 20 units that is not used, a reservoir of sorts. Even with these factors, that means there are still about 30 units unaccounted for. Moreover, I feel like the pump stops bring effective by the time I have 10 units left or in some cases only 15 or 16 units. With my Animas, I regularly used all the insulin in my cartridge. Bottom line, with the Tandem I am flying through my insulin supply.

AS for insulin, I was initially using FIASP and like many of you, I have had some issues so I am now trying Humalog. With both of these insulins I have experienced this gap in what the pump measures versus what I have actually put in. I am also careful to make sure my insulin is room temp before filling a syringe and cartridge (this is a point the Tandem rep reiterated several times).

Secondly, I wanted to ask people about their experience of extracting air from the Tandem cartridges. At present, I follow the instructions provided by the manufacturer. My question is how does one know if all the air is out? I always feel like I can pull out additional air bubbles even when my plunger is fully extracted. Is it possible to pull out too much air or damage the bag?

I hope to return to FIASP (or some mixture of it) but I will save that discussion for a different post. Humalog (and Novalog) is just too slow for me.

Thanks for your insight.

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The pump holds back 20 units from the reservoir meter on the home screen. I don’t know why it does this, it bugged me at first that 20 units just goes missing.

I extract air from the cartridge first, before doing anything else. Usually 5 or 6 times of inserting the syringe and drawing the plunger all the way back and removing the needle from the cartridge and pushing the air out. I then do the 200 fill of the syringe and the remove more air out of the cartridge before filling with 300 units. I’ve never once had an occlusion alarm or have seen an air bubble in the tubing.


I have not noticed any issues with delivery even when my insulin levels get low. I actually ran my cartridge to 1 unit yesterday and it was still working. Blood sugars were steady the whole afternoon.
I also hate wasting insulin so I tend to let it run dry but I also don’t put a lot in the cartridge. My frustration is that I don’t use a lot of insulin but you need to fill it “enough”. So I do sometimes run over the 3 day standard but have never had a problem running 4 days on one site.
As for the air, I just pull out the air until I get resistance on the plunger. Than fill with insulin. Don’t have any issues with air bubbles. But my experiences maybe different from yours. We are all just a different experiment each and everyday.
And of course I will say again, how much I love this system. My life has never been easier! I actively think much less about my diabetes.


I pull air from the cartridge with an empty syringe before I do anything else. I pull the plunger all the way back, and let it sit for a few seconds.
After I fill my syringe with insulin, I stick the cartridge, pull the plunger all the way back, and tap it against my desk. This will create a LOT of small bubbles. I let all these bubbles rise to the top (this helps pull out entrained air.) Then push the insulin in.
This way works perfect for me. I can do this with insulin straight from the fridge with no issues either.

I don’t like wasting it either (despite the fact it costs me nothing) but I don’t want to be caught out somewhere without enough insulin. Shame on me for the handful of times I’ve borrowed my wife’s pump to get a bolus at a restaurant.

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My experience with T:slim cartridges:

I fill 160 ml of Novolog at a time (which lasts me 3+ days) so that I get 6 cartridge fills with nothing wasted in the vial.

I have not experienced delivery problems at low cartridge levels, but have never gone lower than 4-5 units.

To suck out air, I insert my string containing 160 ml, pull back 50 ml to 210. Pull out the syringe to expell the air, insert again, and load. I’ve never experienced air bubble problems.

Good luck,


My new Endocrinologist does not like the way the Tandem pump “treats” the insulin. It is first injected into the bladder of the cartridge, which renders it invisible to the patient for the remaining life of that cartridge. You can’t see if there are bubbles. Then the bladder is squished by a bar that rolls along the bag to squeeze out the insulin. I, too, had weird levels of remaining insulin readings on the Tslim X2. But that wasn’t the worst of it.
My Tandem regularly lost signal control with the Dexcom G6. This could occur if I forgot to wear it with the screen facing outward, if I hugged a pillow to my chest while sleeping with my pump in my sport bra, if I forgot which side of my body the infusion set was on, if I was running and the pump got jostled too much, if I was exercising in normal hot Texas weather and the pump got warm, etc., etc., etc… Sometimes it was impossible to ascertain why the loss of signal alarm would go off. It was stressful. Fortunately, my iPhone never lost signal with my Dexcom. This got me thinking. I could use the Dexcom with any pump device and just make the adjustments myself. Overriding the Tandem closed system to accommodate situations beyond the norm, i.e. real life, was a pain. I’ve gone back to an old manual pump and I use the Dexcom to manage.
Finally, the Tandem people are absolutely swamped with customer support calls. I waited from 2 to 36 hours for call backs on pump malfunctions. The reps were always apologetic but also trained to treat the patient’s complaint as though it’s the first time they’ve ever heard it! I once said, “You’ve got to be kidding! If no one else is complaining about this product, why does it take a rep 36 hours to get back to me? Your phone lines are jammed!” No answer.
If you have a serious complaint with Tandem beyond the 30 day trial period, you will not hear from them. You will become invisible. They will be deaf to your concerns. Do not deal with this company. There are so many other choices. You don’t need a shiny new product that is not backed by a reputable team.

This is factually false. It simply is not true and is made up out of thin air.

I get that you don’t like the Tandem and that should be 100% your choice.

It is awesome that we have three thriving pump manufacturers in the USA with a few more appearing to likely be entering the market over the next couple years.

Choice is good.

But spreading factually false information about a pump you do not like really serves nobody and in all likelihood makes the rest of what you have to say be treated with suspicion.

Tell us about what you like with the Medtronic. I am sure there are lots of features about the Medtronic that you love that other people would truly be interested to hear about.


Wow! Just relaying my personal experience with this pump and the company that makes it. Before calling me a liar on this website, maybe you should understand that people read these entries to inform themselves. How can you, a person I have never met, say that any part of my comment is not truthful? Do you work for Tandem? If so, you’re probably very busy. Stop attacking other posters on this site and get to work.

You are absolutely incorrect about how the cartridge works. @Tim35 is right, spreading false rumors about how a pump mechanically works is not helpful. There are no moving parts inside the cartridge. The whole thing works off of pressure which is why it’s so important to remove all the air before filling the cartridge with insulin.


Thanks for your reply.

I am indeed past the 30 day mark. I want to make it work because when it works, it works great. You are right that what is distressing is precisely this business of not seeing the cartridge to ascertain if there is a problem.

As for loss of signal, I talked to the Rep (as opposed to their 1800 number) and she told me to keep it on the same side as my Dexcom sensor. This has helped a lot especially when I am working out and have it in a pocket on the side of the leggings. I also often wear the pump in my bra and choose the side that the pump is on. It did make a difference.

Glad you came up with a solution.

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Thanks John.

I too have never seen much in the way of air bubbles in tubing (except a few small ‘champagne’ bubbles at the every beginning when I am filling). I am intrigued about your method of extracting air–maybe a youtube video is out there that shows your method.

Thank you everybody for your insights. In this case, it sounds like his/her Endo was misinformed about the mechanics of the cartridge. Really the issue for me is the way the cartridge doesn’t let you see inside it once you put in the insulin. Since I am committed to the Tandem (so many other things to like), I will focus on the air filling process. I don’t see bubbles when I fill my tubing but maybe there is something about the way I extract the air. It sounds like following the instructions that they provide is not sufficient.

Thanks for your reply. I don’t see any bubbles either but perhaps I am not extracting properly.

Thank you for your thoughtful reply. As I mentioned to another poster, I might look and see if there is a video or some visual that demonstrates your process. It perhaps sounds more complicated than it is.

Wow, nice wife. I am kind of obsessive and calculate the night before what my needs will be for the day and if I think I might run out, I will prefill a cartridge.

Yep, she is awesome. I feel quite blessed that she is with me.

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For anybody who has actually used a Tandem pump it is blatantly obvious that your post was factually false.

Somebody who has not used the Tandem pump may not realize that what you posted is simply not true hence it seems appropriate for me to point out the falsehoods from your post.

It would be great if you would refrain from attempting to spread falsehoods.

Perhaps you have some real experiences about the Medtronic which you have said you really like that you could share that people would find helpful.


@JEZ I certainly do not believe that you are intentionally spreading false information, I do feel that you were mis-informed. I detect no malice on your part.

Tandem’s micro delivery system is merely an ingenious piston pump. It has a moving piston that draws in a measured amount of insulin on the uptake stroke then expels it on the on the exhaust. This is my understanding please someone correct me if I am wrong.

Thank you for stepping in. We are all trying to help each other out based on the information we have.

As I have said, I am committed to the Tandem Tslim because my amazing Animas pump is discontinued.

Is it possible for me to redirect the conversation back to the question about how it measures the amount of insulin and how one can know whether air bubbles have been removed from the cartridge.

Thanks to all.