I'm going to suggest a serious algae grazer for your rocks. I like your idea of maybe a tuxedo urchin, or a sea hare could be an option. I have heard they eat a lot, but you may need to return it if your algae stops coming back. An algae blenny could be helpful too. I have a blenny that picks at the rocks all day. My urchin spends a lot of time on the glass, but is helpful too.
I blow my sand and clean every week before water change, and I change the water every week. It sounds like you do already, but I found that doing it strictly every week, sometimes twice a week helped me. I also saw improvement with a small refugium in my sump. I grow a lot of algae and cyano in there now, and it is harder to clean in my opinion. I'm not sure if you could make macro work or not. I think lfs water is a red herring, and I also think 25 nitrates is not that big of a problem.
FS