Wow, that's quite an impressive algae infestation. It actually looks nice on the driftwood!
Usually algae is a problem when a tank is cycling or recently cycled but that is obviously not your reason.
Sometimes reducing the level/time of the daily light helps but won't be a fast fix. I assume the tank isn't in natural light? You dont use fertilisers or CO2 do you? Has it got worse over time or stayed fairly steady?
There are a number of commercial 'antl-algae' products available widely, not sure where you are based. I haven't tried any though as mine has always cleared naturally shortly after 'cycling' but has been a different algae?
Simon