Watersprite is taking over the aquarium! It's a nice problem to have.
The stems had grown up to lie across the water surface, blocking some current flow. So I thinned it out today- cut out stems in the back that were getting sucked into the filter intake, snipped off baby plants with their roots, to let float free, cut back the tallest stems to an inch or two below the surface and removed a few inner fronds that were dying from lack of light- being blocked by their own foliage!
I left some of the bigger cuttings to float, too. Not sure if they'll grow roots also, but it doesn't hurt to wait and see.
The worst plant in the aquarium now is the amazon sword- seen here in front. Its bigger leaves keep dying back. I think it just likes more nutrients than I'm providing- or it's too close to other root systems.