I believe you're experiencing the "diatome (sp?) bloom" which I believe is pretty normal for a newly set-up tank. I also understand that if water is within standards and lights are not on excessively, that it will go away on its own. I've also heard having good flow will help keep it in check.
I had it and it started to fade, then increased again when we added our fish, probably due to a little extra feeding and having the lights on, and now it looks like it's starting to fade again.
Search and you'll see many pictures of it so you can see if it's the same thing you're going through.