It's splitting.
Noticed about a week ago(after lights off for a while) that it seemed to have a huge mouth, or what looked like a mouth. All the tenticles/arms/feelers were in a ring around the middle. But I guess I never noticed until today that it was splitting down the shaft/stalk/stem too, from the top down.
This morning while putting on my boots, I looked up at the tank and there it was. A doughnut sitting ontop of a Y. I instantly knew it was splitting. Don't ask me how, I just did.
Hopefully I'll get a picture before the grand finale.