Well, I was an idiot today.
I was using a syringe to suck up some water in my 2 gallon to rinse the duckweed from behind the filter, not really paying great attention, and bam, I managed to suck up my betta. Thankfully I got his tail, and not his body (if one can be thankful for such a thing). But now he has a hole in the middle of his tail where a chunk of the fin was torn away and I have major guilt. I've never seen a fin injury quite like this (normally you see tears from the edge, not holes in the middle), so I'm not sure if he'll heal correctly.