my guess would be they are accustom to the full tank water pressure.when the "TIDE" goes out they scramble to find a place where the Pressure was what they are accustom too.
12 inches of water = 0.436 psi i would suspect they are sensitive to 3-4 inch change in water pressure.
Ah, never considered the change in water pressure. Should I be concerned, especially if I take some time to refill the tank? Normally, as soon as I add fresh water back, they calm down pretty quickly and resume to their normal selves.
For reference, it looks kinda like this vid (not mine): https://www.youtube.com/watch?v=s7EEa1iXiYQ
My amano's do that every time I do a 50 percent wc also. Sometimes I have to be careful because it seems like they are very attracted to the vac end and have actually sucked up a few in the past but they scoot right out of the tube and have no ill effects. It almost looks like they enjoy the whole wc thing.