If it is spot algae, it will be tuff and most fish just can't peal it off. Your glass will take some elbow grease

.
Do a search on this site for algae and you will see some great posts on dealing with it.
Do you have live plants? If you happen to I can relate a personal finding that along with my regular ferterilizer application that adding potassium once a week in a small dose made a huge impact on all green algae reduction.
If you are seeing large amounts of algae then something is out of balance (lights, feeding, circulation etc). Again, in my opinion a fast growing plant like Wisteria will do wonders in depriving algae of growing nutrients.
For my part, I know I will always have to put up with a small amount of spot algae and just clean it off. My tank does not get direct sun, but is certainly in a bright room. I do have fish that work on it, Ottos do seem to try and so does the Bushynose Pleco, but I always have to follow-up with a scrub every couple of months.