[Tandem t:slim] Insulin discrepancy after switching from Fiasp to Humalog - missing ~40 units?
Hey everyone, I’m trying to figure out if this is normal behavior with the Tandem t:slim or if something weird is going on.
I recently switched from Fiasp to Humalog in my pump. Before, with Fiasp, I noticed some discrepancies in insulin remaining, but now with Humalog it seems even more noticeable.
Example from last night:
- Filled cartridge with ~120 units around 6 PM
- Used about 12 units for tubing/fill process
- Overnight + this morning I used roughly 14-15 units total
So in theory I should’ve had around 90+ usable units left this morning.
Right after installing the new cartridge, the pump only displayed “60+ units” instead of an exact number - which has been normal in other cartridge changes. However, this morning it showed “40+ units,” and after a small bolus it updated to exactly 55 units remaining.
I understand the t:slim always has some insulin left in the cartridge that won’t actually be usable, and I know the pump estimation isn’t perfectly accurate. But a discrepancy of ~35–40 units seems huge to me.
Also, I haven’t noticed any visible leaks at all unless there’s some kind of micro leak that wouldn’t be noticeable externally.
What’s making me question it more is that this has now happened for two cartridge changes in a row since switching insulins.
Has anyone else experienced this, especially after switching insulins?
Would love to know if other t:slim users have seen something similar.