Cant get Phosphates down

[WindowMaker]

Hi all,
I have been combating algae issues for quite some time and seem to have hit a stand still.

I run RODI
I run GFO
I run filter socks
I run a euro reef skimmer

nitrates and nitrites are undetectable

I have constant battles with red algae, It is frustrating the crap out of me. I also have started getting buildup on the glass again (this had stopped for a while). My hanna checker reads at .05

any other things I can do to attempt to curb this? I am reaching my wits end...

thanks for your help.