How to Use Aluminum Sulfate in a Swimming Pool. Your pool might have cloudy water for numerous reasons, but if it's due to excessive minerals, clean your pool with aluminum sulfate. It has a positive charge when it's dissolved in water and attracts the negative particles until they solidify into chunks, making it easier to clean the water.
Check the alkalinity of your pool. The alkalinity must register more than 75 milligrams per liter as calcium carbonate for the alum to work.
Backwash your filter according to the instructions for your filter. Sand filters use a different process than DE filters, and you can use alum only with sand filters. It can damage DE filters.
Add the recommended dose of aluminum sulfate for your pool to the most convenient entry point before the filter. This is normally the skimmer, but add it slowly because it can become localized there, rather than moving all the way to the filter. Read the instructions that come with your aluminum sulfate, but a good rule of thumb is to add 2 oz. of alum for every square foot of area on the pool's surface.
Clear your filter of sediment after a few days. Repeat the process until the cloudiness caused by minerals is gone.