As you have discovered natural sunlight is good for a lot of algae. The problem with sunlight is that most of these corals grow in places that get 12 hours of direct sunlight in relatively shallow areas of water (reefs). Depending on where your house is it probably isn't going to be enough. I live in the northeastern quadrant of north America. During the summer we get about 8 hours of good direct sunlight on the south side of our home but that's it. During the winter the sunlight is much weaker, not nearly enough to sustain coral. The windows are also a potential problem here because of the temperature fluctuations. Hot during the day, cold at night. Tropical reef fish don't deal well with that sort of fluctuation. There are folks experimenting, with some interestingly good results, with channeling skylights into their tanks through aluminum ducts. The only one I've ever seen pics of, I believe, was out of Melbourne AU. Very cool... But very expensive set-ups.
