Can someone tell me what the cause of this is?

[Ashleyyvance]

I need help bad and quick. Within the past week my water has turned green. All my perameters are fine and I did a 50 percent water change when I noticed the green it went away for about two days and now it's back again. I have a 300 gallon and a lot of money invested not sure what is happening.

[Good_GReef]

Algae bloom though I've never seen one take over the water in mine like a freshwater tank i once had. Happened on a vacation once and total loss of life. Maybe a lights out routine or other members can chime in. Also, is it possible your bulbs are getting old or do you run leds? Using RO water only?