Algae underneath glass tops. Remedies besides scraping?

[hrdneglcry]

I keep glass tops, and have several tanks over 100 gallons. Algae has always grown on the underside of the glass tops.
I am wondering if anything is sold that can be safely sprayed on the underside of the glass when it is clean that will keep algae from growing on it. Or do I just have to live with the maintainence of cleaning it by hand when it grows?

[papagimp]

Live with it. You can try macro algae in a fuge to attempt to outcomete the nuissance algae growing on that glass, but being that high up towards the lighting, Not sure if it'll do any good or not. Stock up on some elbow grease and have at it.