I've been fighting it in my tank for a while now. You might want to try bumping up your turbo snail numbers. In my 55 g I recently went from two snails to six and it seems to help. They seemed to ignore my rocks for the longest time then "discovered" them and now spend a lot of time grazing the rocks. The good thing about snails is they're cheap and a good addition to the tank regardless.
The other thing I've been doing is every couple of days I pull as much algae off the rocks as I can with my fingers and remove it from the tank. My snails and crabs then seem more likely to graze on the areas with shorter algae. They tend to avoid the really long strands.
The Tang may or may not help. I added a yellow one to my tank thinking it would mow down the green algae. It seems to eat every type of algae it can find except the long green stuff.
How old is your tank? I notice a lot of people, myself included, seem to report green algae problems right around the one-year mark. Maybe it's part of the algae cycle?
Keep at it. After almost two months of frustration I seem to be finally getting rid of much of the green algae. I don't know if it is more snails, more water changes, my tank maturing or a combo of all.