WOW! It is a long time since I have heard anyone suggesting daphnae to get rid of green water. Excellent suggestion. Here in central Iowa, there are enough decades of pesticide use that daphnae are a bit rare nowadays. As a little tyke, i often found daphnae in water-filled cow hoofprints in my dad;s pasture. Sounds like you folks up North have purer surface waters than we do. I'm envious. :-)