Day not even four for this cartridge. :-( The insulin has decided it wanted to go bad this morning. I was like what in the WORLD is going on, I kept correcting and no results. Yep I feel like garbage with a headache. I guess after being outside most of the weekend and one really warm and humid afternoon/evening on Saturday, I just cooked my insulin. This NEVER happened with my Medtronic pump. In fact I could use insulin in the same cartridge for over 7 days. With the tslim, in my experience, my insulin will not go past four days. I am on Humalog but I wonder if switching to Novolog would help me stretch it out more. With this pump I am almost never changing my site and insulin at the same time. Has anyone out there had good luck with Novolog in a tslim going past 4 days?