Pieris. The "pink" parts are new leaves.

Ah, cool... apparently found all over the US too, and anywhere that's "wet" enough, though I've never seen one (or maybe just not this nice hehe). It seems to be growing fine potted in soft substrate in the aquarium with full-spectrum lighting (and near the window). The turtles like docking on it :)

No need to wait until spring. It's a popular house plant here. Easy to grow from cuttings. They'll root in water.

Sounds like it’s ditching the old leaves that had grown in more light and is replacing them with new ones better adapted to the lower light. I think your symptoms would be different if it was a watering issue or a reaction to the fertiliser, you’d have yellowing leaves and brown patches and drooping etc. I don’t know how the artificial light complicates the picture, I’ve never used one but hopefully someone who has will chime in. Maybe overall you now have more light in total and it’s ditching the old leaves to make way for ones better for higher light? Not so likely... It’s a lovely big tree :)