Here is a really good picture of it.....
http://www.botany.hawaii.edu/reefalgae/What plants look like/Plants Dictyota acutiloba.htm
Frick, I didn't remember seeing anything like it in your tank. But like I said, I'm still debating how bad it really is

The weekend before I left, I managed to over dose my tank with RO/DI, my salinity was down to 1.019. I slowly raised it over three days. Also, the Wed before I left my CO2 ran out

so when I replaced the CO2, it wasn't exactly dialed in, I went low, figuring I didn't want too much, I'd rather go with a little lower. That combination most likely killed off some micro infauna and other things. I've had this dictyota for a while now, it didn't pop up overnight, it's been about 10 days of growth since the last pruning.
Seriously though, some of the corals that are amongst the thickets do look really nice once I prune back the dictyota. Therman has said in the past that dictyota is a great breeding ground for fauna/infaua. Yeah it looks horrible, but if I didn't have it, what would have happened to my tank last week. Trates sky rocket, everything dies, who knows. It's kind of like caulerpa, but I don't know about and toxins it may or may not produce.
Some people have given me advice in the past to try a Naso Tang (not ready to add another tang to my 120), sailfin lawnmower blenny (don't want to press my luck with the bicolor I already have), I have one urchin (came in on LR from the gulf) that I don't think touches it, and I just got a foxface wabbitfish last night (I'll tell you about his progress in time) and I've been told about freshwater injections for it(that hasn't helped in my case) I did notice when cleaning my power heads, that vineger seems to kill it pretty well

I think my main problem might be my water, I need to replace my DI. I'm also going to start dosing Kalk in hopes to precipitate some phosphates, if there are any. Last night I took out a gallon of dictyota, I think it looks alright now......
That's my plan right now

Gareth