A few things...
The overfeeding isn't helping. Cut back to at MOST once per day. And when you feed, just put a little in and let them eat it all, then put more in... let them eat it all... you get the idea. Don't just dump a cube of food in and walk away. You could even cut back your feeding to once every two days and your fish won't suffer.
No need to buffer fresh water. When doing top offs, just use the RO
water straight - don't add anything.
What kind of corals do you have? Depending on what corals you have, the phyto might be useless to them and just fouling up the tank.
What's a protein skimmer? Probably something you should have. It removes organic waste from the water before it can break down into nitrates. Here's a good start for looking into one: http://www.google.com/search?q=protein+skimmer
Can you get a picture of the algae? That would help us know what we're dealing with...