Update #16:
I'm officially declaring the cycle done. Ammonia is negligible, and nitrates are present. The coralline has stopped dying off, and there is a nice crop of algae growing. Only one problem.
Bryopsis.
The algae that is growing is very wavy and delicate like hair algae, but there are also distinct "feathers" visible. This is a horrible picture, but maybe it'll help to give a general idea about the growth form...
The feathers make me think
B. plumosa, but I'm not entirely sure. It covers large patches of sand and rock and even the glass, and seems to grow from small bases which eventually turn into a mat. When the "feathers" get long enough, the flow picks up a piece and spreads it around the tank, ensuring that it can't be isolated. My plan of action is to
a) Try emerald crabs. I don't think that six will cut it as originally planned, so I'll double that amount.
b) Dose some reef flux. I'd like to keep chemicals out of the tank if possible, but it seems like I might need them.
c) Try a scribbled rabbitfish or fox face. I understand that this fish is generally thought of as being too big for my tank, but it will be the only large algae eater in there, and there is a fair amount of flow. I think it'll be ok.
I hope that I can dispose of this menace, but from what I'm reading, it's worse than bubble algae. Does anyone have experience getting rid of the stuff? Thanks!