Planted Tank Guru
Join Date: Jul 2010
Location: British Columbia, Canada
If it is in fact green dust algae, i.e. it's mostly on the glass of the tank and is easily wiped off - then a UV sterilizer will deal with all of it that you can get free-floating into the water column. I got rid of it by wiping it off daily for several days in a row, so that the bulk of it was into the water and the UV could pick it up & zap it.
You still have to remedy the problem long term by determining the root causes & dealing with that, but the UV will kill off all the free-floating material it can take in via it's in-take filtering process.