The glass on the hoods, between the lights and water has grown a large amount of algae and a lot of hard water stains.

The algae was easy enough to remove by scraping with a razor. But this had little impact on the white build up.

What would be the best method for removing this build up?

I have this problem too. I use comet and a cleaning pad and that works okay. I've thought about trying lime-away. It builds up so fast and i bet it really affects how much light actually gets to my tank.