The more I read another thread the more I think I have mustard algae too. I have had no trouble controlling my water for the past three years. This year it is a mess! I had it crystal clear but was still getting some settling on the bottom when my pump was off at night. I am worried about the high chlorine shock levels needed in my VIG pool. My CYA is high (67 at the pool store) from using trichlor over the winter in an injector. After putting my solar blanket on for a week, I pulled it back to see green stuff on the walls. I put in 4 gallons of 6% bleach and brushed. I added more the next day to keep it up. Is all this chlorine going to eat my liner? The water is clearing but I have been this route before. Isn't there anything else to kill mustard algae? I can't give you a precise FC reading because my tester won't read that high. It's a dark burnt orange color.