Found another nimble spray this morning, about 1/2 again as big as the one I killed last week. Also, definitely saw the black tips on end of mystery crab, which pretty much IDs it as a gorilla of some type. Will put together a trap tomorrow and see if I can trap them -- the LFS can feed them to whatever eats them. Or, could be that someone will want them.
The thing moving along the bottom rock was indeed an anemone and it has taken up residence next to the yellow ball sponge. Given its tattered appearance, I suspect this is one that survived my attempt at culling last week. Hmm.
Way more algae growth over the weekend. The snails are slowly cleaning up the walls, but the bottom sand is positively lush with growth. I did my first water change this morning -- and ordered a phosphate test kit, too. I may do a couple more small water changes this week to get the water in better shape.