How To Remove Dead Algae From Pool Bottom (and Keep It Out)

Dead algae can cause more algae blooms, not to mention how gross and cloudy the water will look. It’s important to remove dead algae as quickly as possible to prevent the liner from getting damaged. Fortunately, you likely have most of the chemicals and tools needed for the job.

To remove dead algae from the pool bottom (and keep it from returning), follow these steps:

• Add shock
• Use an algae killer
• Run the pump
• Vacuum the pool
• Try a water clarifier
• Clean the filter
• Brush the pool walls
• Add an algaecide
• Maintain the pool’s chemistry

Throughout this article, I’ll explain exactly how to get rid of the dead algae in your swimming pool. I’ll also show you how to prevent that pesky algae from ever coming back.

Add Pool Shock to the Water

Free available chlorine often turns into chloramine when it encounters algae. While the algae is dead, it makes the pool look cloudy and inactivates the chlorine in the water.

It’s crucial that you know how often you should shock a pool and how much chlorine is needed to eliminate the algae. If you don’t add shock after removing the algae bloom, another will arrive.

I recommend using Pool Mate Pool Chlorine Granules to add pool shock.

They come in an eight-pound bucket and include 55% available chlorine. It’s strong enough to get rid of algae and prevent it from coming back, but you don’t have to worry about it being too harsh for vinyl liners. Three ounces of this granulated chlorine treats up to 10,000 gallons of water.

Here’s what you should know about clearing a pool with shock:

• Not all shocks are created equally. Always check the percentage of available chlorine to know if it’s worth buying. Powder pool shock shouldn’t be below 50%, whereas liquid chlorine needs to be above 10%.
• Almost all granulated chlorine will make your pool look cloudy for a little while. The granules take a couple of hours to dissolve. Additionally, the dead algae often cloud the water. Circulating the pump will expedite the process.
• Adding pool shock is an integral part of removing dead algae from the bottom of the pool. The dead algae is often a food source for living algae, which nearly guarantees high levels of microscopic algae in the water. You’ll need to eliminate the bloom before clearing the water.

Use an Algae Killer to Remove Excess Algae

Leftover algae are often too small to see. The pool could be covered in dead algae, but there are almost always living algae in the water. Your best bet is to use an algae killer to get rid of the rest of it.

Unfortunately, many pool owners confuse algae killers with algae preventers. Both products are typically labeled as “algaecides,” which makes things difficult. The best way to know is to read the label to know if it eliminates or manages algae blooms.

Green to Clean by Coral Seas is my favorite algae killer. It comes in a two-pound and a four-pound container. Two pounds of this product treats 15,000 gallons. However, it doesn’t hurt to double up with Green to Clean to ensure you eliminate all of the algae.

Here are the instructions for using Green to Clean in a 15,000-gallon swimming pool.

1. Pour half of a pound of shock into the pool.
2. Pour half of a pound of Green to Clean around the edges.
3. Turn on the pool pump for 24 hours.
4. Repeat the previous three steps.
5. Use a water clarifier to remove all of the dead algae from the water.

While this process is fairly straightforward, it needs to be followed closely for the best results. If you don’t think you need to get rid of excess algae, read on for the remaining steps and suggestions.

Circulate the Swimming Pool

Running the pool pump is the most important part of owning a pool. None of the chemicals work without water circulation.

Furthermore, the water has a much higher chance of preventing algae and getting rid of dead blooms if it’s moving. Your filter can’t catch anything in the stagnant water, nor can the skimmer basket or pump basket.

I suggest running your pool pump for one hour per ten degrees Fahrenheit outside. Remember to use the outdoor temperature, not your pool’s temperature.

You can get a variable-speed pump to reduce the energy, speed, and utility bill cost of running the pump. Circulating the pool at lower speeds for longer periods of time is always better than high speeds for a short amount of time.

Run the Pool Cleaner

Pool vacuums work by using suction-side or pressure-side mechanics to trap debris, including dead algae.

Robotic pool cleaners don’t need your pump’s suction since they rely on an external electrical outlet.

However, all three options are adequate for the removal of algae. Make sure you know which vacuums your pool is suitable for.

While automatic pool cleaners are the best option for any other scenario, manual vacuums are the top choice for removing dead algae. You can brush the bottom of the pool while suctioning the debris into the skimmer basket, pump basket, and filter.

It’s a surefire way to know what’s being removed without waiting for an automatic vacuum to roll over to the right spot.

My favorite vacuum head for removing algae is the Swimline Weighted Flex Vacuum Head. It attaches to any universal telescoping pole and a series of hoses, and it sticks to the pool without lifting up unnecessarily. I also enjoy the rolling wheels that glide across the surface rather than dragging and clouding the dead algae.

I suggest running your pool vacuum a couple of times per week if possible. Algae always start on a microscopic level, so it’s ideal for removing it before it blooms. Suction-side pool cleaners send all of the debris into the filter. You’ll have to clean it more often if you prefer this vacuum type.

Try Water Clarifiers

Pool filters are always removing excess debris from the water. They get rid of oils, algae, dirt, etc.

However, some pool filters can’t remove extremely small debris. For instance, sand filters often catch anything bigger than 20 microns. Cartridge filters can remove down to 10 microns, and some DE filters can remove as low as 8 microns.

Contrary to popular belief, bleach won’t clear up a cloudy pool as fast as water clarifiers and shock. Most household bleach solutions contain 5% chlorine, which is much lower than the recommended 10% to 12% found in liquid pool chlorine.

Instead of relying on bleach, I recommend using a water clarifier. Pool clarifiers attach themselves to the filter media, drastically improving their ability to catch microscopic objects (like algae). Sand filters can be as useful as high-quality cartridge filters with the right treatment.

I like the Robarb Super Blue Swimming Pool Clarifier, which comes in a two-pack of 32-ounce bottles. Each ounce can clarifier pools up to 5,000 gallons, so you’ll have more than enough for multiple treatments.

Run the filter for eight or more hours after using this clarifier, and you’ll be impressed by how much of the dead algae is gone.

If you want to use a pool clarifier, keep these tips in mind:

• Brush the bottom of the pool before using the clarifier to circulate the debris into the filter.
• Always run the pump when using a clarifier, or it won’t do anything.
• Not all clarifiers can be used with all filter types (however, the aforementioned Robarb clarifier works with any filter media).
• Most water clarifiers will increase your filter’s PSI, so don’t worry if it goes a little higher.

Clean the Filter

Dead algae get caught in your pool filter. If you don’t clean the cartridge, DE, or sand in the filter, you won’t be able to remove any of the dead algae.

Furthermore, the clogged filter limits the pump’s capabilities and makes it much more difficult to stir the chemicals throughout the swimming pool.

If you have DE or sand, you should know how to backwash your filter. Backwashing the filter media compresses it, preventing you from having to change the DE or sand too often.

However, you can’t backwash a cartridge or quad-DE filter. Instead, you’ll have to spray off the cartridges. Once you clean the filter, it’ll have much more room to catch the dead algae.

Try these suggestions to catch more dead algae in the filter:

• Replace the cartridges if they’re torn, or the bands are broken.
• Always clean your filter after removing dead algae because it can grow back.
• Remove the debris from the vacuum bag if it’s a pressure-side cleaner.

Brush the Pool Walls

You should always brush the pool’s walls and bottom whenever you have to remove dead algae. The scrubbing action lifts the dead algae spores into the water, helping the pump and filter do their job. Brushing the dead algae also activates the chlorine and helps it tackle small spores.

Here’s what I suggest for brushing the dead algae out of your pool:

• Brush from the bottom upward to keep the dead algae off the bottom of the pool. The scrubbing motion will push the algae to the top layer of water, pushing it toward the skimmer basket.
• Use a soft bristle brush for vinyl and fiberglass pools. Stiff brushes can damage the soft material, leading to rips and wrinkles.
• Use a stiff bristle brush or wire brush for plaster pools. Plaster swimming pools often get black algae that push deep into the porous surface. The wire material lifts the dead black algae from the plaster quicker.

My favorite brush for removing algae is the Whale Wall Classic Swimming Pool Brush. Here’s why:

• It’s an 18-inch brush with a unique tail design, and it’s perfect for any pool surface.
• The rear tail improves the momentum, suctioning to the wall and blowing the dead algae toward the skimmer.
• It’s a universal brush that fits any universal telescoping pole for brushes and vacuum heads.

If you don’t have a good brush for algae, I recommend picking this one up.

Add an Algaecide

Adding an algaecide will prevent the dead algae from encouraging new algae growth. Many algaecides are copper-based and citrus-based for their acidic properties.

However, there’s a new form of algae prevention that relies on removing algae’s primary food source: phosphates.

If algae don’t have food, they won’t be able to spread. You might experience a few small blooms here and there, but it’s almost impossible to have massive algae blooms if you use a phosphate remover.

Natural Chemistry Phosfree is a great phosphate remover, and I think it’s one of the best chemicals you can put in your swimming pool.

This pet-safe, swim-safe formula goes directly into the skimmer basket to remove algae’s food source before a big bloom. Every time you run the filter, the phosphates get caught in the media and don’t cycle back into the pool.

Whether you prefer the tried-and-true copper-based formula or the modernized phosphate remover, algaecides are incredibly important. Nobody wants to be on the edge of another algae bloom every summer month.

Algae preventers are much more affordable than fighting a dangerous, gross-looking algae bloom. You also won’t have to deal with dead algae.

Maintain the Swimming Pool’s Chemistry

Your pool’s chemistry is crucial. Dead algae will leave phosphates in the water, encouraging algae blooms down the road. However, maintaining the pool’s chemicals will keep the algae in check and prevent future blooms.

So, what are the five points of maintaining a pool’s chemistry to handle dead algae?

1. Keep the pH between 7.2 to 7.8 to help the chlorine remain as effective as possible.
2. Maintain chlorine levels from 1ppm to 4ppm or 5ppm to 6ppm if you’re fighting an algae bloom.
3. Don’t let the TDS (total dissolved solids) get above 2,000ppm, or it’ll be very difficult for your chemicals to dissolve and get rid of the dead algae.
4. The alkalinity should range from 80 to 120.
5. The phosphates should always be below 100ppb (parts per billion).

Your pool’s cyanuric acid should be between 40 to 90. The CYA (also known as pool conditioner) provides sun protection for the chlorine in the water.

Without enough cyanuric acid, the chlorine will evaporate before it can clear the dead algae. However, you need to lower the cyanuric acid if it’s above 100 because it will limit the chlorine’s effectiveness.

Jonah Ryan

Jonah has worked for several years in the swimming pool industry installing and repairing equipment, treating pools with chemicals, and fixing damaged liners. He also has plumbing and electrical experience with air conditioning, ceiling fans, boilers, and more. When he’s not writing for Temperature Master, he’s usually writing for his own websites, LawnCareLessons.com and DIYByHand.com.