Understanding the Difference: Algaecide vs Clarifier for Your Pool

That sparkling blue water in your pool doesn’t happen by accident, and there’s a bewildering range of products on offer, each one with its own role to play. It’s not only the clarity of the water that’s important but also the control of bacteria and other contaminants that affect the health of those using the pool. Algaecide and clarifier are often grouped together, but each serves its own purpose in a unique way.

Algaecide vs. Clarifier – an interesting comparison. Both play a part in maintaining the pool’s health, but that’s where the similarity ends. Algaecides prevent algae growth but don’t clarify the water whereas clarifiers don’t kill algae but help remove fine contaminant particles clouding the water.

To give you clarity (pun intended) regarding the use of algaecides and clarifiers, I’ll make an in-depth comparison (another one), which will include a definition of each product, their purpose, how best to apply them, and their respective pros and cons. As a pool owner, you’ll then be better informed when deciding which of the products will be most beneficial in keeping your pool in tip-top condition.

Algaecide Vs. Clarifier – A Full Product Comparison

Both products are available in various forms, each with its own properties to suit different situations. I’ll avoid getting too complicated in examining all the variations and concentrate on the most important.

Algaecide Vs. Clarifier – Definitions

Algaecides are chemical compounds that prevent and control algae growth and are used mainly in pools but also in ponds, lakes, and other bodies of water. They contain active ingredients that smother or poison the algae. They are used as a backup after high-dosage chlorine shock treatments, which kill algae and other bacterial contaminants in the pool.

Clarifiers are chemical products formulated to improve water clarity by binding together tiny particles of debris, including dead algae, that are suspended in water and cause it to look cloudy. By doing this, the larger particles become easier to remove either by filtration or by vacuuming them from the pool floor where they have settled.

To summarize, algaecide and clarifier each have different functions, with algaecide designed specifically to eliminate algae growth while clarifiers improve water clarity by helping to remove suspended particles of debris that create cloudiness in the pool.

Algaecide Vs. Clarifier – Application And Use

Algaecides are most effective when used a day or two after a shock treatment of the pool when chlorine levels have returned to normal. Depending on the type of algaecide, they can last for a few weeks in summer and for several months in winter when algae growth is slow.

The role of an algaecide is to weaken the algae by suffocating or poisoning the cells, making it easier for the chlorine in the water to kill them. So, adding algaecide after shocking the pool is part of the maintenance program of your pool and is done regularly, from weekly to every three weeks during the swimming season.

Once applied and well-circulated by running the pump for a few hours, an algaecide will remain effective even when the pump is off.

Clarifiers are only required when the suspended particles in the water become so numerous that it becomes hazy or cloudy. Applying the clarifier is not a regular part of maintenance and is only done when necessary, which may be monthly or even less often, depending on how much the pool is used.

Remember as well that the clarifier is effective only if the pump is left to run for twelve to twenty-four hours after application so that the treated water passes continuously through the filter to enable it to remove the larger particles.

For this reason, I recommend keeping algaecide and clarifier separate. You can buy them combined into a convenient 2-in-1 product, and given that they can be combined, it’s okay to apply them at the same time. However, because the algaecide will produce some debris as it attacks the algae, I suggest waiting 30 minutes before using the clarifier.

The algaecide is usually introduced around the perimeter of the pool, while the clarifier can be added at the return nozzle if in liquid form, put into the skimmer basket, or broadcast over the whole surface of the pool.

Algaecide Vs. Clarifier – Chemical Composition

Understanding the difference between algaecides and clarifiers and how best to use them means knowing the different types of each and how they achieve their purpose.

Algaecides Come In Three Forms

  • Quats or Quaternary ammonium algaecides attack algae cell membranes from within and disrupt them, causing the death of the algae. Excessive use may cause foaming, but this is the least expensive form of pool algaecide.
  • Polyquats or Polyquaternary ammonium compounds are longer-lasting than quats, twice as effective, but more expensive. Non-foaming and non-staining, they work by coating the surface of the algae cell and suffocating it.
  • Metal-based algaecides are usually formulated using copper ions, which are positively charged and attach to the algae cells, entering and poisoning them from within. These are the only algaecides that kill black as well as green algae but also can cause staining.

Clarifiers Have Several Variants

  • Polymer-Based Clarifiers utilize special polymers with a highly positive charge density that bind particles together into larger masses, making filtration systems more effective in capturing particles.
  • Natural Clarifiers are formulated using enzymes and other natural positively charged ions called chitosan, which are extracted from crab shells, are particularly effective in attracting organic and inorganic particles and oils in the water.
  • Blended Clarifiers contain a mix of enzymes, chitosan, and polymer ions, together with phosphate removers, that effectively combine the benefits of all the ingredients in one product.
  • Flocculant Clarifiers achieve the same end result as clarifiers, so I’ve included it here, although some experts differentiate between the two. The difference is that a flocculent combines the particles faster and into bigger clumps, which then sink to the bottom of the pool and need to be vacuumed rather than removed through the filter.

Algaecide Vs. Clarifier – Compatibility

Algaecides should be applied to pool water about 12 to 24 hours after shock treatment when chlorine levels have returned to approximately 2-4 ppm. In most cases, both the algaecide and the shock will become ineffective if the two are mixed or applied too close to each other in time.

Clarifiers are generally compatible with other pool chemicals, but I recommend you check the manufacturer’s instructions on the packaging before combining the clarifier with anything else.

Algaecide Vs. Clarifier – Summary

Here’s a table that summarizes the main similarities and differences between the two products:





Prevention of algae growth

Increased clarity of pool water by removing particles of organic and inorganic debris


Breakdown of algae cells through smothering or poisoning

Combining suspended particles into larger clumps, which are removed by filter or vacuuming.

Chemical Composition

Non-metallic polymers or copper ions

Chemical polymers, natural enzymes, and chitosan


Regular preventive maintenance every 1-3 weeks during swimming season

Only when symptoms require treatment


Typically added directly to water

Added to water or skimmer basket


Depending on the temperature, between one week and five months

Each treatment is temporary and must be repeated when necessary.


Algaecide and clarifier, both essential ingredients in the maintenance of the pool, are different in many ways but often grouped together in discussing pool treatment. They are also combined in pool care products, but because of their different treatment schedules and interaction with other additives, they are more effective if applied separately in your efforts to keep your pool sparkling, clear, and free from algae.