I've got a ZooMed thermometer/humidity gauge that sticks to the inside glass of the tank.
In the water changes I haven't seen ANY specks floating in the water. I did manage to get her out and be handled once since she's started acting wonky, and looked her over really well around the eyes, heat vents, close to the folds of her mouth, etc. Haven't seen anything. She really enjoyed having a tablespoon of vegetable oil added to her water dish (she completely submerged a couple of times for a few seconds), and it made her slippery and shiny for a day afterwards, but I would hate to treat more aggressively for mites if it isn't mites.
The undertank mat is just outside of her hide, so that she has a warm spot, a medium warmth spot, and a cool end to the tank.
My only other guess was that the once a week feeding was too much for an adult (she's almost 3 feet long ...) even if she was accustomed to it, and is just soaking after feedings to make her skin feel better. Kind of like people unbuttoning their pants after they overindulge, you know? Especially when I read about BP's only defecating once every month or so and mine has already done so twice since I got her. She gets even more aggressive when we go past the 7 day schedule, so I've been wary of extending the time between feedings.
Thanks!