I got green water really bad in my 450 Litre. I bought a uv filter (rated for 300L tanks) and used algea fix but still took a while to go away. Then when the tank was just recovering we had to get a powerpole replaced. They told us when we were rushing out the door an hour before they turned it off. The power was out for 6 hours and the tank is still a bit cloudy 2 weeks later.