Pool Sand Filter Not Filtering Algae


Pool Sand Filter Not Filtering Algae

No pool caretaker can afford to overlook the undeniable truth: algae present a perpetual challenge. Despite meticulous care and precise water chemistry balance, pools remain vulnerable to the relentless encroachment of these microscopic invaders. Thriving under conditions often beyond our control—be it scorching temperatures, oppressive humidity, or ceaseless rainfall—algae defy easy eradication.

Even in death, algae exhibit a remarkable resilience, persisting as a tenacious adversary in the ongoing battle of pool maintenance. Despite diligent efforts involving scrubbing, cleaning, and filtering, many pool owners relying on sand filters encounter the frustrating reality: these filters often prove inadequate in removing expired algae effectively.

The consequence is dishearteningly familiar: a resurgence of contaminants into the pool, undermining the efficacy of all previous efforts. To address this challenge, one potential solution involves redirecting the vacuum’s output to the “Waste” setting. In the subsequent discussion, we shall delve into the intricacies of techniques designed to efficiently eliminate and filter out algae from pool filtration systems.

How a Pool Sand Filter Works

A sand filter pump sucks in the water, pushes it through the special filter sand with force, and pumps the filtered water into the pool.

Dirt such as algae and insects remains in the sand filter. In this way, you can easily prevent the pool water from being polluted.

The suitable filter sand consists of grains with a circumference of 0.4 to 0.8 mm. If the grains are smaller, they can end up in the pool. If the grains are larger, the filtering will not be as accurate.

In the situation where the sand filter isn’t filtering the algae, the best sand filter troubleshooting solution is to add 1/4 cup of diatomaceous earth into the filter. Turning to flocculants can also help.

Filter sand lasts an average of 3 years before it needs to be replaced.

First, we’ll tell you about the right procedure for removing algae from the pool and then reveal what to do if the sand filter wouldn’t filter out the algae before returning the water into the facility.

Step By Step Instructions

When it comes to algae in the pool, many think directly of algaecides and disinfectants such as chlorine. These chemicals are not really suitable as a means against algae in the pool. It takes a few more steps to completely remove the algae.

Our step-by-step instructions are suitable for all three types of algae (black, green, and yellow algae).

Step 1: Disinfect and Wash Everything

The algae were somehow brought into the pool. Algae cells can get caught on swimwear, toys, air mattresses, equipment, and others.

It would be very annoying if you laboriously fight the algae infestation only to then carry them back in. So find all swimsuits, bathing toys, swimming trunks, parts of your diving equipment, and plastic balls and clean them.

Wash the clothes in the washing machine. Use a strong detergent on the rest of the items and scrub them off with a brush.

Step 2: Test the Water

Check the water weekly. Before you deal with the algae problem, you should also do a water test. Use simple test strips or a test kit for this. The most important values ​​are the chlorine content (FC), the pH value, and the alkalinity (TA).

Step 3: Maintain Correct Pool Chemistry

With balanced pool chemistry, the values ​​are in these areas:

  • pH: 7.2 to 7.6
  • Alkalinity: 80 to 150 ppm
  • Chlorine content: about 3 ppm.

Step 4: Brush Like There’s No Tomorrow

Scrub the algae off the pool walls. If you do this carefully, the disinfectant can penetrate deeper into the remaining algae. In your work, focus on the areas that are particularly rich in algae. The intensive scrubbing allows you to quickly remove the pool algae from the bottom.

Step 5: Manual Suction

Set the valve to “Waste” and then suck the algae out of the pool. You lose a lot of water in this process. Therefore, focus on the areas that are particularly heavily overgrown with algae.

If there is really a lot to vacuum, you should run fresh water into the pool at the same time using a garden hose.

Step 6: Do a Strong Shock Chlorination

For proper shock chlorination, you need calcium hypochlorite pool shock – and not too little of it. Follow the directions on the packaging to determine the dose for a normal pool shock. Multiply that dose by two, three, or four, depending on the type of algae you’re dealing with.

  • Green algae: double the dose
  • Yellow or dark green algae: triple dose
  • Black algae: four times the dose

Step 7: Filter the Algae from the Water

Check the water level, then set the valve to “filter” and switch it on. Let the pump run for at least eight hours.

Step 8: Brush and Shock Again

Before doing another shock chlorination, you should scrub the pool walls again. Focus on the places where the algae first appeared.

Black algae, in particular, have roots. Even if they are removed, they can reappear later.

A single dose is sufficient for this final shock chlorination.

Note: The water may be still cloudy the next morning. This cloudiness is likely a side effect of the last shock chlorination. Use clarifiers to clear these up quickly or just wait for the water to clear on its own.

Step 9: Clean the Filter

Clean the filter. Under no circumstances should you rinse it out. After all, the last thing you want now is to gradually flush the algae back into the pool water. Therefore, clean the dirty pool filter thoroughly with a filter cleaner.


How to Filter Out Algae in A Pool Sand Filter 

You can use flocculants to remove algae if you spot them in the facility early on. The flocculant saves you a ton of work and money by combining the chemical with the algae particles and making them easier to suck out of the pool.

If you only have a slight problem with green algae, treatment with flocculants is sufficient. If there is serious algae infestation from green algae or other species, you should rather follow the cleaning schedule which involves vacuuming to “Waste”.

Step-By-Step Instructions

  • Turn off the pump.
  • Set the valve to recycle. In this way, the flocculant is quickly mixed with the pool water.
  • Add the recommended dose of liquid or powder flocculant.
  • Turn the pump on again and let it run for at least two hours.
  • Switch the filter pump off again and let the water stand overnight. During this time, the flocculant binds to the algae cells, precipitates, and collects at the bottom of the tank.
  • The next morning, set the valve to “Waste” so that dirty water does not flow back into the pool.
  • Connect the wastewater hose.
  • Vacuum the pool. Proceed slowly and carefully so that you don’t stir up the debris from the floor too much. If the water gets too cloudy during this step, you need to pause briefly and let the particles settle again first. Always add water with a garden hose when vacuuming.
  • If there is a lot of algae: Brush the walls of the pool.
  • Perform shock chlorination with double the dose of shock.
  • Let your filter run for at least eight hours.


In conclusion, achieving the optimal algae-free state in a sand-filtered pool is a multifaceted task that hinges upon a blend of crucial factors. In the pursuit of pristine pool water, the key ingredients encompass a judicious understanding of pool chemistry, the employment of a proficient pool brush, the diligent use of a vacuum, and, perhaps most paramount, the deployment of a robust sand filtration system.

Through the elucidation provided earlier, we have delved into the intricate process of effectively eradicating algae from a sand-filtered pool. It is our fervent hope that you can now embark upon this endeavor with the utmost confidence, equipped with the knowledge and tools necessary to restore the sparkling clarity of your pool water.

Wise Reviewer

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