We too have had algae problems this summer. Made the mistake of leaving the early 20's kids in charge of the pool chemicals for 10 days while we were out of town. Took almost 3 weeks to get it back in control. Our pool people told us if the algae is bad enough that you can't see the bottom, you need to add 4x the regular dose of shock. I about fell over, but it did the trick. Needed to do a lot of brushing and vaccuming afterwards, but it did work. Crystal clear and sparkling water now, which is just how I like it.