I second on the coffee filter trick. I hiked in a swampy marshy area that had a ton of algae. After the first round of filter left me with green tinted water, I filtered a second time with the coffee filter and it came cleaner and most of the wierd tast went as well. On that trip it was very warm (30*C, 90% humidity) so I didn't use my stove much. Boiling the water in the evening for a full hydration bladder isn't much fun.