my pond is 7 months old and is still muddy. I was thinking about trying alum or gypsum to solve this problem. The pond is approx. 1/2 acre and is 7.5' deep at the deep end and 3' at the shallow end, so I guess an average depth would be 5'. How much alum or gypsum would I need and where do you get it? What would be the best to use?