Hi,
Actually algae is a sign of healthy tank! It is good for the fish--extra nutrition since they like to nibble it. But it does look bad.
What experts suggest is to scrape it off the front and sides (I use a sponge like scrubber thing I got at Petsmart) and leave it on the back. That way, you can see your fish

but still have the benefit of algae which is a good thing!