I have 300 gallon of water volume, and have some algae on my corals. I run a two little fished 150 with gfo for phosphates. It has always seemed that my nitrtates stay high, would like to lower them to see if my sps corals would color better.
In this hobby, the only thing you need is a box with salt water. Everything else is up for debate. I would try NOPOX or some other carbon dosing to see if that would help your nitrate problem. Go slow, your tank looks fine to me...