It's normal for 2-3 days – especially if you have "normal" reef lights that have a really wide spread. The glass ends up being
really well lit and grows quite a bit of algae. The good part about it is that it's the easiest algae in the tank to clean. Use it to your advantage rather than fighting to eliminate it. I like to let it get
really thick occationally to "scrub the water" and then scrape it down for the fish or snails to eat.
Speaking of that, how's your cleanup crew right now? (specifics!

)