I have very muddy water. I was wondering and its prolly already been talked about a lot but here goes. If I get the alum. and it gets all cleared up how long does it last? Is it like pond dye and go away when the rain hits. A little background pond is about 10 years old and always muddy. Maybe 6 inches is all you can see at best. I would love to get this cleared up some just don't want to dump money into it for it not to last.