What is the difference between flocculant and clarifier?

Flocculants and clarifiers both work on particles too fine for the filter, but flocculants form large clumps that often sink to the bottom and must be vacuumed out, while clarifiers form small aggregates that the filter gradually retains. Flocculants are faster and suitable for very cloudy water; clarifiers are gentler and suitable for slightly hazy water.

The two terms are often confused, including on some packaging. Yet, choosing the wrong product, or using the right one with the wrong method, can waste you time and water. Experts in aquatic environments since 1998, we set the record straight.

What they have in common

Cloudy pool water contains suspended particles so fine that they pass through the filter media: dust, pollen, organic residue, traces of creams. They carry small electrical charges that keep them dispersed in the water.

Flocculants and clarifiers neutralize these charges so that the particles stick together. In both cases, larger aggregates are obtained, which are easier to remove. The difference lies in the size of these aggregates and how they are disposed of.

The essential differences

The flocculant

It creates large clumps. Depending on the product and method, these clumps are either retained by a sand or glass filter, or heavy enough to sink to the bottom of the pool. In this second case, filtration is generally stopped during settling, and then the sediment is slowly vacuumed out, with the valve in the waste position, directly to the drain.

This is the fastest solution for very cloudy water, but it requires care: vacuuming must be slow, and it causes water loss that will need to be compensated.

The clarifier

It forms small aggregates, just large enough to be retained by the filter. Filtration remains running and does the work, over several hours or a few days. No sediment to vacuum, no water loss, but a more gradual result.

It is suitable for slightly hazy water or regular maintenance, when you want to keep sparkling water without heavy intervention.

How to choose?

Before choosing between the two, make sure the problem is indeed caused by suspended particles. Cloudy water can also reveal a pH that is too high, insufficient disinfectant, too short a filtration time, or a clogged filter. In these cases, neither flocculant nor clarifier will permanently solve the problem.

• Measure the pH and disinfectant level with a test kit.
• Check that the filter is clean and that the filtration time is adapted to the water temperature.
• Assess the cloudiness: can you still clearly see the bottom of the pool, a little, or not at all?
• Then choose a gentle product for a light haze, a flocculant for very cloudy water.

Products and their dosage

The dosages below are those indicated on our product sheets. For any other product, refer to the label.

• CTX-41 liquid flocculant: preventive or curative, filtration running and with no swimmers. 1 L per 100 m³ for cloudy water, 0.5 L per 100 m³ as a preventive measure. Leave to work, then vacuum with the valve in the waste position.
• CTX flocculant cartridges: placed in the skimmer, they gather microparticles to facilitate their capture by the filter, for slightly hazy water.
• CTX natural flocculant: made from chitosan, it clarifies cloudy water with weekly use. 8 ml per 10 m³ per week, filtration running for at least six hours after application.

The right method for each

With a flocculant, by settling

1. Balance the water and clean the filter.
2. Pour the product according to the label, filtration running for a few moments to distribute it.
3. Leave to settle without swimmers, for the indicated time.
4. Slowly vacuum the sediment, valve in the waste position.
5. Top up the water level with fresh water, then rebalance the pH and disinfectant if necessary.
6. Clean the filter by backwashing to remove the clumps that may have been trapped in it.

With a clarifier or a skimmer product

1. Clean the filter and check the pH.
2. Add the product to the skimmer or distribute it in the water, according to the label.
3. Let the filtration run continuously for the indicated duration.
4. Backwash to remove the retained particles.

And for a spa or garden pond?

The distinction between flocculant and clarifier also exists outside of classic pools, but the products are not interchangeable. A spa, with its small volume of hot water and its cartridge filter, requires products specifically formulated for it. A natural pool or an ecological swimming pool, without chlorine, has its own products, compatible with the biological life of the water.

For a garden pond, you can find dedicated clarifiers, such as Aquipond ClearWater, which promotes the grouping of particles to facilitate their recovery by mechanical filtration. Its product sheet recommends checking the water parameters and the state of the filtration before using it. Never use a product for chlorinated pools in a pond populated by fish or plants.

In all cases, the rule is the same: a product designed for your type of installation, a dosage compliant with the label, and filtration in good condition.

Common mistakes

• Overdosing: an excess of product can worsen the cloudiness instead of reducing it.
• Treating unbalanced water: the product works poorly if the pH is outside the recommended range.
• Vacuuming the flocculant sediment too quickly: it becomes resuspended.
• Forgetting to backwash after a filter treatment.
• Combining several products without checking their compatibility.
• Swimming during treatment, contrary to the instructions on the label.

One last mistake, more discreet: using flocculant then clarifier just a few hours apart because the result is slow. Leave the first treatment for the time provided by the label, check the water, then decide. The two products work on the same particles, and combining them does not speed anything up.

If you have already overdosed a flocculant, our article on the removal of flocculant sediment guides you.

Prevention rather than cure

The best treatment is the one you do not need to do. Well-filtered and well-disinfected water rarely becomes cloudy. A few habits limit the use of flocculants and clarifiers:

• Adapt the filtration time to the water temperature.
• Check the pH and disinfectant at least once a week during the season.
• Regularly empty the skimmer and pre-filter baskets.
• Perform backwashing according to the indications of your filter manufacturer.
• Cover the pool when it is not in use, to limit the input of dust and leaves.
• Replace the filter media when it is worn out.

Frequently asked questions

What is the difference between a flocculant and a clarifier?

The flocculant forms large clumps, often deposited at the bottom and then vacuumed. The clarifier forms small aggregates that the filter gradually retains, without vacuuming.

Which one works faster?

The flocculant is generally faster. The clarifier works more gradually, at the pace of the filtration.

Can you use a clarifier with a cartridge filter?

Gentle-action products are better suited to this type of filter than flocculants, which quickly clog the cartridge. Always check the compatibility on the label.

Should you stop filtration with a flocculant?

This depends on the method. With settling, you stop filtration while the clumps sink. With filtration, it remains running. Follow the product label.

Do flocculants and clarifiers replace disinfectant?

No. They improve the clarity of the water, but do not disinfect it.

Can you use a pool flocculant in a fish pond?

No. Use only products designed for garden ponds, compatible with fish and plants, and follow their label.

Also read

• Removing flocculant from a pool: vacuuming the sediment and rinsing the filter
• Sediment at the bottom of the pool: identifying each sediment and removing it
• How to choose a sand filter for a pool?