over two weeks' time

the appearance of my forty gallon has really altered. It looked nice enough

but then suddenly swamped with brown algae- diatoms?

I rubbed a lot off, trimmed off the worst of the now-dying plant leaves, and cut back the rotala wall because its lower half was all blackening- no way I can rub off those tiny fragile leaves.

Now it seems to be coming back around but looks awful empty.