This is from a recent post on the same topic:
I know of no chemical to add to get rid of the stuff.
Have you checked the age of your lights? Old lights shift in spectrum and up comes the icky green.
What kind of lights do you have. In my tank Bryopsis loved VHO actinic, so I got rid of it. Also if you have lights for dawn/dusk, you can leave the main light on for only 5 or 6 hours, but the supplement lights on longer.
I don't know if you would see a result from turning the light off for 2-3 days.
Have you added macro algae to the tank/sump to uptake the nutrients that the bryopsis is using?
Have you blasted the rocks with a powerhead, to get all the gook off them, and filtered the tank with a canister filter at the same time?
After you pulled the stuff off the rock, have you put the rocks back in the tank upside down - so the bryopsis gets no light?
Have you been underfeeding the tank?
You could move all the live animals to another tank (or into the sump - with lights of cours- if you have one) for a while and leave the lights off in the main tank for several weeks. I think setting up a small tank would cost less than thrashing the main tank with chemicals.
There is no quick fix to this problem that I know of. Sorry. I recently beat it, so it can be done.
If you do a search on bryopsis you will see much discussion on it. The search function is very useful. Also a search for "Service Temporarily Unavailable" will get you results on that question.
You may also want to check out this thread for some useful info.
http://www.reefs.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=1&t=032855&p=
Welcome to R.O!
RR