Green water

[Stasher]

Ok, I have a question on for my brother.
He has a 90g with about 12 1" or smaller africans/s.american cichlids in it. The tank is around 3 months old. He is using 2 hagen 802 ph's in the tank for movement and has both a Fluval 304 and 404 for water filtration. His water has been tested constantly and the parameters are all in line.

The problem is that the water in the tank is a cloudy green and you can't even see the back of the tank. He is doing extreme water changes to battle the color of the water but is having no luck. He just did a 75% water change the other day and by the next morning the water was completely green again.

He is unfortunately using tap water but can't afford an RO unit at this time. What can be causing this water born algae bloom. The glass, rocks and sand in the tank are extremely clean, the water is the only problem in the tank. They have reduced feedings significantly and lighting also.

Thank you for any insight into their dilema.

Chris