With a high-light style tank, your plants will be using up quite a bit, if not all of the available nutrients in a short period of time. This means algae can thrive! Having .5 Phosphates isn't too bad. You could certainly bump it up just a bit. But you could be lacking in Nitrates (NO3) too. Here's a good article that helped me out when I was first trying to understand fertilizers and the (roughly) ideal PPM's of your planted tank. See if it helps, and ask as many questions as you need to!
Sorry- didnt see the link to your quote. Can you repost?