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How Does it Work:

Aluminum Sulphate, or “Alum”, can be used to clean a murky, cloudy pool without having to drain the pool water (a method called “Floccing”). It is a double salt with a strong positive charge, which when used correctly, attracts suspended particles. These particles group together to form heavier clumps that sink, and then your filter removes the sunk particles.

Important Notes Before Using:

  • Only for use with Sand Filters (does not work with DE Filters or Cartridge Filters, as it clogs the small pores of the fabric).

  • You must be able to vacuum the waste, and cartridge filters or filters with slide valves do not normally have this option.

  • Best used on pools that do not have a lot of heavy debris like leaves, twigs (or if your pool does, ensure to manually remove the large debris before starting the process)

** We at Steveston Chemical Solutions are not pool experts and have just compiled recommendations/instructions based on the articles referenced at the end of this post that we hope are helpful. We always recommend conducting your own research for your specific needs. Please consult an expert if you have any questions or concerns**


This process works best with water temperature of at least 70°-80° F, whoever can work in cooler temperatures if needed.

  • Remove any large debris from the water.

  • Test the pool water and balance the pH and other chemistry to normal levels.

  • Backwash your filter according to the instructions for your filter for an initial cleaning.

GENERAL Overview of Use (Detailed Instructions Below)

  • Increase the water level.

  • Equalize the pH to about 7.0.

  • Add flocculant to the pool.

  • Let the pool pump run for a few hours.

  • Turn off the pump and let it sit overnight.

  • Turn on the pump.

  • Vacuum the bottom of the pool.

DETAILED Instructions:

Method One: Using Alum on Pool Surface

  1. Follow Preparation Steps above. Also check the alkalinity of your pool. The alkalinity must register more than 75 milligrams per liter as calcium carbonate for the alum to work.

  2. Spread 4 lbs of Alum over the pool surface, per 10,000 gallons (though depending on how much debris is in your pool, you can use between 2-8 lbs per 10,000 gallons).

  3. Put your multiport valve on recirculate and run pump for 2 hours, during this time the contaminants will clump together. Brush sides and bottom of pool to loosen clumped particles.

  4. Turn off pump for 12-24 hours, or until the Aluminum Sulphate settles to pool floor. Your pool should look fairly clear with a thick layer of sludge at bottom.

  5. If your pool pump is on a timer, remover the “on” timer so that the pump will not turn on automatically in the morning and disturb the settled alum.

  6. Set your valve to waste, and let it vacuum the debris.

  7. Add hose to your pool as you are vacuuming waste to replace water lost during vacuuming.

  8. As your filters begins to filter out particles, you will need to clean them frequently to ensure they do not clog. You may need to clean the filters a few times a day in the first few days, then less as time goes on.

  9. Test water pH and chemistry and adjust as needed.

Method Two: Using Alum in Sand Filter

  1. Follow Preparation steps above, but also raise chlorine levels to 10% of Cyanuric Acid Levels. Also ensure when backwashing the sand filter for the initial cleaning to make note of the pressure gauge reading.

  2. With filter running, pour 6 oz of Aluminum Sulphate for every 100 lb of filter sand in the tank. Add the Alum directly into the filter tank.

  3. Backwash when the filter pressure rises to 8-10 lbs above starting pressure. The rise in pressure is because the debris has clumped together and is starting to clog the filter.

  4. Vacuum the pool to collect the debris that has escaped the filter.

  5. Test water pH and chemistry and adjust as needed.

Articles Referenced:

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