To clean a cloudy pool, aluminum sulfate is often the method of choice. It works in a unique way to help the pool water clean itself, saving you time and making the filtration system more efficient.

Aluminum Sulfate is a product better known as Alum. Alum is a white powdery flocculent that when circulated in your swimming pool water, quickly clumps all the fine particles in your cloudy water, including green algae, into particles large enough that the green algae sinks down to the bottom of your swimming pool, clarifying your pool water. Then you simply vacuum the bottom of your swimming pool and all the green algae in it to waste.

We do not recommend using Alum in pools that have Cartridge Filters.


The main reason for cloudy pools include:

  • Water balance: If the pool water isn’t correctly balanced you may face cloudiness.
  • Poor filtration: There are many reasons for poor filtration, starting with inadequate filter size, problems with hydraulics, inadequate pump size, short filtration cycles, old filter media, etc.
  • Pool surrounds often contribute particles such as leaves, bugs and other organic material, which break up in the pool water.
  • High bather load: Bathers obviously bring things like dirt, dust, lint, suntan lotion, skin cells, etc into the pool.
  • Algal bloom.
  • Heavy rain.


For swimming pools and spas, a Flocculant will attract suspended particles to itself, resulting in marble sized clumps that sink slowly to the bottom of the pool. The filter pump remains off during treatment, and after 8-12 hours a thick white carpet needs to be slowly vacuumed – to waste.

Aluminum Sulfate is a double salt with a strong positive charge. Particulate matter in solution have negative charges. Over the period of several hours, the alum molecule attracts suspended particles. Eventually it grows to a large size and heavy weight, until it slowly sinks to the pool floor. It works best with well balanced pool water, and in water temperatures of at least 70° F. The tricky part of using alum is that the aluminum hydroxide precipitate must be vacuumed to waste the following day. Alum is considered a flocculant, because it sinks material to the floor - as opposed to clarifiers, which enlarge particles only slightly, for trapping within your pool filter.


So here’s how you’ll use alum in your pool:

  1. Skim, vacuum and brush the pool to remove large debris.
  2. If the water level is a bit on the low side, add a bit from the tap to bring water up a bit higher than normal.
  3. Test water pH and use a pH Increaser to bring the water’s pH up to about 8.0 – this is critical in getting alum to perform at its best. (Raising pH alone will help bring some of the particles suspended in the water out of solution, dropping them to the bottom.)
  4. Run in normal “filter” mode for 1-2 hours after adjusting up pH.
  5. Shut the filter/pump off for 12-24 hours– this is also very important.
  6. Broadcast over the surface of the pool as evenly as possible at the rate of 500g per 10,000L of pool water.
  7. Wait until morning (the Alum settles to the pool floor) and vacuum pool with multiport valve set to “waste” or “bypass to waste”.
  8. Add more fresh water as needed and adjust pH if necessary.


  • You must be able to vacuum to waste.
  • Cartridge filters or filters with Slide Valves don't normally have this option.
  • Read our earlier blog post for options on vacuuming to waste, even if you don't have a multiport valve on your filter.
  • When vacuuming to waste, it must be done slowly, to avoid disturbing the layer, which has the consistency of wet toilet paper.
  • Add a hose to the pool to replace water lost to vacuuming to water.
  • If you don't have a multiport valve, don't run the pump after adding the alum, as it will clog your filter fast.
  • Use a pool brush instead to create circulation in the pool, and help distribute the alum.
  • You can use any kind of Aluminum Sulfate (aka Aluminum Sulphate) - food grade, technical grade or garden grade - just be sure not to use Ammonium Sulfate, which is a different chemical.
  • The dosage of 4 lbs per 10,000 gallons is an average amount. Depending on the amount of solids in the pool, effective dosage can be 2 lbs to 8 lbs per 10,000 gallons.
  • If your pool pump is on a timer, remove the 'ON' tripper, so that the pump won't come on in the morning, and clog your pool filter, or disturb the settled alum.
  • If there is algae present, you can add 2 - 4 lbs of shock per 10,000 gallons, immediately after adding the Alum. Alum is most active in warmer water temperatures of 70-80°F, but also works in colder water temperatures.


Don't let aluminum sulfate touch your skin, and wear safety goggles and gloves while you're working with it. Alum can cause chemical burns.

Pool Chemicals Delivery is not available for East Malaysia (Sabah/Sarawak) addresses.

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Pool Flocculant - Alum (50kg/Bag Aluminum Sulfate)

  • Product Code: AL0012
  • Availability: 50
  • RM289.00
  • RM195.00

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Tags: Aluminum Sulfate, Alum, Swimming Pool Chemicals, Flocculant

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