I'm so proud of him!
I had a feeling he wasn't making them before because the airstone in his tank didn't keep his water still enough. I unplugged it last night because it was acting up and making unusual sounds, plus I don't think Geist was ever crazy about it in the first place.
Well, this morning I went to feed him and found a tiny cluster of bubbles around one of his silk plants that goes to the surface. Unfortunately he has to come home with me today for spring break, and that means I need to clean out his tank and get rid of his nest. =< Hopefully he'll make a new one once he's settled again.