For alum to work properly as a water clarifier (not a sand filter aid), the pH of the water needs to be near 7.0. At a pH near
8.0, the floc is unstable and begins to come apart. If the pH is below 6.5, the alum can dissolve in the water making it
worthless. The pH should be adjusted to near 7.0 - 7.2 before adding the alum.
Estimates vary on how much alum to use for water clarification. The reason is that the amount needed is dependent upon
how much dirt and suspended particles are in the water. A consensus is between 4 and 8 pounds per 10,000 gallons of
The amount can then be mixed up in a bucket of water, made into a slurry and added around the perimeter of the pool or
dry alum can be broadcast directly into the water. After the pool water has circulated for 4 hours or when the pressure
gauge on the filter reaches the manufacturers maximum, turn the circulation equipment off. The settling out of the floc will
occur during the next 6 to 12 hours. Once the floc has settled to the bottom, it should be vacuumed to waste. Be careful not
to stir up or disturb the alum floc on the pool bottom. The pool water lost due to vacuuming should be replaced and the
Total Alkalinity and pH should be readjusted to their proper levels.