The problem is with water source, tap water probably has lots of NO3 and PO4. No matter how many times he/she does water changes, NO3 and PO4 always brought back into the tank.
1. I would use RO/DI first to filter the water. 2. I would dump in 8-16oz of Brine shrimps, in less than a week, brine shrimp consumes all the algae, provided the fish doesn't eat them.