I had a cloudy water problem this spring, also. Just shocked it to 25 ppm and kept it there for 2 days, then let it come down to 10ppm for a week.. It cleared right up. so, I think you're on the right track. Keep in mind that this only works if algae is the cause for cloudy water. There are a couple other things that can make water cloudy. I read somewhere that if the alkalinity is high, say 200 or more, it can cause the calcium to precipitate in the water. Also, while others here have fared well adding DE powder to a sand filter, I have not. On 2 occasions this year, DE caused my water to go cloudy. I had to give the filter a good couple of backwashes to get it out. Then the water cleared. Good Luck.