One thing depending on what kind of water he is using for his WC and what his current phosphate lvl is, doing WC may not do anything . I have helped alot of people who had "green water" that was free floating algae that feeds on phosphates. they were using tap water that the phosphate lvl was almost as high as there tanks lvl. If your tank is going threw a algae bloom in the water itself best bet is a UV on a tank that size.