Question
I have a 500 gal pond, cannot stop the water from turning green. Pond is covered by lattice on top gets perfect amt. of sun shade. It was 60% covered with plants, all kinds I removed all but lily still green. Have treated with micorb lift and algaefix. Pump is 900 gal per hr, I clean the filter
every 4-5 days. I am stumped never had this problem before.
Fish are doing fine, ph ~6.5.  

Answer
The simplest solution would be an ultraviolet clarifier.  It exposes the algae that passes through to radiation, keeping it from reproducing, and also killing it.  This is only good for the tiny, free-floating types of algae, and not any that are attached to rocks or liner.  The next option is nutrient control, which is much more involved and takes some trial and error.