Slipper Tongue coral

[Dingo Dog]

I've had my slipper/tongue coral for about 3 years and it's always been very happy. I've done nothing out of the normal, yet about 2 months ago I began noticing that occasionally it becomes more plump/puffy than normal. So much so that it becomes buoyant enough during the course of the day that it slightly floats just enough to move a tiny bit with the current.

I've checked my water and everything is where it should be, I even have baby sponge popping up on my LR. So, please share your experiences on this coral.

Thanks in advance.