What is Pool Flocculant and When Should You Use It?



If you’ve ever faced cloudy water issues, you’ve probably come across flocculant as a possible solution.

In this article, we’ll give you the skinny on pool flocculant, how it actually works, and when it might be worth using to clear up your water.

Short answer: Pool flocculant binds to small particles in your pool, causing them to clump together and sink to the bottom so they can be vacuumed out. It only works on non-living living contaminants, however.

What is Pool Flocculant?

Flocculant (floc) is a substance that binds small particles in your water together, and it’s often used to restore water clarity in a pool.

This process, known as “coagulation”, combines particles into heavy clumps of matter that quickly settle on the bottom of the pool where they can be vacuumed up and removed from the water.

These clumps are made up of non-living organics such as very fine dirt, dead algae, and various cosmetics small enough to escape filtration, but still contribute to cloudy or discolored water.

Note: Flocculant does NOT work on living organics such as live algae, bacteria, and viruses, and is not a replacement for your pool sanitizer.

How Does Flocculant Work?

Flocculant is essentially a “chemical magnet”.

When you add floc to your pool, you’re introducing positively-charged particles that seek out and bind to negatively-charged particles.

Fortunately, in the context of a dirty or cloudy swimming pool, most of the tiny negatively-charged particles are unwanted contaminants that managed to sneak by your filter.

This particle attraction snowballs into larger clumps that eventually sink to your pool floor where they can be removed.

What’s the Difference Between Flocculants and Clarifiers?

Flocculants and clarifiers are very similar.

Both use particle attraction to form clusters of tiny matter, and both allow you to remove contamination that’s too small for your filter.

Where they differ though, is in aggressiveness.

Clarifier not only works slower (over several days), but it also forms considerably smaller clumps that remain light enough to stay suspended in water, allowing them to be circulated and eventually filtered out.

Flocculant works very fast (in around 24 hours), works on larger particles, and forms bigger, more visible clumps that are too heavy to stay suspended in water, allowing them to be easily vacuumed out.

When Should You Use Flocculant in Your Pool?

Flocculant makes sense only after eliminating the root cause of your cloudy water problem; otherwise, any improvement gained is short-lived as new particle matter soon begins to accumulate.

As usual, that means nailing the basics.

Testing and rebalancing your water—including your pH level, total alkalinity, and calcium hardness—is often all that’s required to restore water clarity in the majority of cases.

If that doesn’t do it, it’s probably a cleanliness issue. Look at increasing your sanitizer level, brushing and vacuuming the pool, cleaning your filter, and keeping your pump running for a full 24 hours.

Once all potential causes have been addressed, using a flocculant (or even a clarifier) is a suitable next step for clearing up any remaining debris.

Does Your Filter Type Matter?

Absolutely, it does!

Remember, flocculant is specifically designed to deal with contaminants that are too small for your filter to process. The more “stuff’ that gets through your filter, the more reliance you’ll have on flocculant.

Here’s a quick overview of each filter type:

Basically, flocculant plays a larger role if you have a sand or cartridge filter, whereas it has little to no impact if you use a DE filter since it’s already capable of filtering out those extra tiny particles.

Note: You can put DE media in a sand filter to improve the filtration. It won’t compare to a dedicated DE filter but it’ll be a notable improvement.

How Do You Use Flocculant in a Pool?

Here’s how to use flocculant, step-by-step:

  1. Test and balance your water, ensuring pH, total alkalinity, calcium hardness, and free chlorine are within their ideal ranges.
  2. Set your filter valve to recirculate. This will ensure water bypasses your filter media during this process, preventing blockages inside your filter. If you don’t have this setting, see our notes below.
  3. Add flocculant to your pool. This process can vary so just follow the dosage instructions on the label based on your pool capacity.
  4. Keep your pump running for around 2 hours in order to properly circulate the flocculant throughout the pool.
  5. Turn the pump off and allow at least 12 hours (or overnight) for the flocculant to work and the clumps of debris to settle.
  6. Set your filter valve to waste and vacuum the debris using a suction-side cleaner or manual pool vacuum. Alternatively, you can use a robotic cleaner to do this independently from your filtration system.
  7. Check the water level and fill the pool if needed (vacuuming to waste/drain may remove a fair amount of water).
  8. Turn the pump back on. You’re done!

Note: If you can’t recirculate your filter, keep your pump off and dilute flocculant in a bucket before pouring it evenly around the perimeter of your pool. Wait at least 12 hours and turn the pump back on only AFTER vacuuming.

Can You Swim After Using Flocculant?

Yes, it’s generally safe to swim after using flocculant.

Flocculant manufacturers tend to dance around exact timeframes, but floc is used in such small doses that once diluted in your pool, it’s no longer considered harmful to humans.

However, as with adding any chemical to your water, always allow reasonable time for partial dilution. This may only take a few minutes if it’s applied broadly and while your pool pump is in full swing.

The Bottom Line

Most water quality issues in a swimming pool can be resolved without resorting to flocculant, but it certainly has its place.

As long as you’ve ruled out balancing issues, algae formation, and other cleanliness issues, using flocculant to coagulate any remaining non-living organics will often work a treat.

Categories: Pool Care, Pool Chemistry