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What are Pool Clarifiers?

Swimming pool clarifiers are pool chemicals containing positively charged molecules, which are mutually attracted to negatively charged particles. Nearly all water clouding particles have a negative (anionic) charge, and are drawn to the positive (cationic) clarifier chemical.

Like a magnet, pool water clarifiers begin to coagulate immediately, growing from a microscopic size of under 1 micron, to a clump of 30 or 40 microns in size, which is easily removed by most pool filters.

Use pool clarifiers for issues with cloudy or hazy water, after spring opening or an algae bloom, for example. They are helpful for pools with poor circulation and filtration or lax sanitation, however if you need to use clarifier regularly, consider improving these aspects of your pool water treatment.

Pool clarifiers are made from water-soluble cationic polymers like quaternary ammonium chlorides or polyacrylamides. Natural pool clarifiers make use of chitin, a natural polymer derived from crab, shrimp and lobster shells. Aluminum sulfate is another type of clarifier; in a sub-group of flocculants.

How to Use Pool Clarifiers

STEP 1: Balance your pool water. One of the most frequent causes of cloudy pool water is poor water balance. High pH, high Alkalinity, high Calcium hardness can all make it easier for dissolved solids to come out of solution. Poor water chemistry also makes it difficult for your chlorine to do its job of oxidizing contaminants and particles in the pool water.

STEP 2: Read the Instructions. Pay attention to any water balance recommendations; test and adjust your water chemistry as needed. Follow dosing instructions very carefully, using the marks on the edge of the bottle, to add only the recommended dosage. Over-dosing the pool with too much clarifier can create the opposite effect, acting as a dispersant, not a coagulant.

STEP 3: Run the Pool Filter 24/7. As much as possible, run your pool filter for a faster pool clean-up. Pool pumps are built for ‘continuous duty’ service, and can be run 24 hours per day without problems. If your neighbors complain about the pump noise, cut it back to 16 hours per day, or build a temporary shelter around your equipment to deflect the noise.

  • Dilute clarifier into a bucket of water and pour around the edge of the pool.
  • Backwash or clean the filter only after the pressure gauge rises 7-8 psi.
  • In days to follow, maintain good water balance and high chlorine levels.
  • If needed, vacuum or brush the pool daily to remove settled particles.
  • If needed, re-dose the pool 5-7 days after the initial clarifier treatment.

Difference between Pool Clarifier and Flocculant

A pool clarifier and pool flocculant (aka Floc) are similar, they both act as coagulants to coalesce small particles into larger clumps.

The difference between clarifier and floc, is that clarifiers work over several days to grow particle sizes large enough for your filter to remove. Flocculants work much faster and quickly grow into very large clumps that will clog a pool filter, so they must be used differently.

Clarifiers work with your pool filter running, all night if possible. With flocculants however, after adding the floc, you shut the pump off overnight. The coagulated clumps become so heavy that they sink to the pool floor. The following day, the pool is very slowly vacuumed to waste. In order to use pool floc, you must be able to vacuum to waste.

Aluminum Sulfate, or Alum is a granular flocculant, also used for garden soil pH amendment. Use 4 lbs per 10,000 gallons, broadcasted across the surface with the pump off, and vacuum to waste the following day. Alum can also be used with sand filters as a filter aid, to dramatically improve filtration temporarily, until the next backwash.


Cloudy pool water can be a hazardous condition; divers cannot see the pool floor and can mis-judge the depth, and pool owners cannot see if something is lying on the bottom of the pool. Cloudy pool water may also be harboring harmful bacteria.

Use clarifiers or flocculants as needed, to restore water clarity or to help poor-performing pool filters. If your pool is still hazy after 5 days; recheck water balance, chlorine level and filter operation and apply another dose of pool clarifier, being careful not to over-dose.

Not all pools use pool clarifiers and flocculants; if you need pool clarifier regularly, look at installing a larger or more effective pool filter, running the pump longer each day, and/or improving water balance and sanitation efforts.