How Much Algaecide to Put in a Pool? Expert Advice

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Owning a pool is a joy—until algae turn your crystal-clear water into a murky mess. That’s where algaecide comes in. But, how much algaecide to put in a pool?

KEY TAKEAWAYS

• Chlorine kills algae, algaecide weakens them. Both are essential for algae-free pools.
• The right algaecide dosage is key: Too much causes foaming/staining, too little is ineffective.
• Dosage varies by product, pool size, and algae severity. Always follow product instructions.
• Run the pool filter for 2-4 hours after adding algaecide for proper distribution.
• Increase algaecide dose after shocking, opening/closing, or heavy rain.
• Use algaecide to prevent algae, not treat an existing infestation. Shock a green pool first.

Use too much algaecide and you will end up with foamy water and staining. Use too little and it won’t stop the algae from spreading. It’s frustrating, especially if you’ve spent hours cleaning and balancing the water.

Algaecides are essential for effective pool maintenance and algae prevention. But, you must know how much algaecide to put in a pool.

Using too much algaecide can cause foamy water and staining while using too little won’t stop the algae from spreading. 

This guide will walk you through everything you need to know. You’ll learn about the types of algaecide, how to calculate the correct dosage and the best way to apply it for clear, healthy water. 

Whether you’re a new pool owner or a seasoned pro, these tips will ensure your pool stays algae-free and sparkling all season.

What is Pool Algaecide and Why Is It Important?

What is Algaecide?

Contrary to expectation Algaecide does not “kill” algae. Chlorine does the killing. But, chlorine needs the assistance of an algaecide to be an effective killer of algae. 

Algaecide weakens algae making it easier for chlorine to kill them. Algaecide does so by disrupting energy transport, cell division, or the cell membranes of the algae.

Think of algaecide and chlorine as a team fighting to keep pool algae at bay. Algaecide makes the first move by weakening algae and the chlorine moves in for the kill.

You need adequate levels of both if you do not want your once-clear water to turn green, cloudy, and slimy.

Types of Pool Algaecide

Algaecides are complex chemicals but not all algaecides are the same. Here are the four most common types:

• Copper-based Algaecides: Highly effective against tough algae, like green pool algae. However, overuse can stain pool surfaces.
• Quat (Quaternary Ammonium) Algaecides: Affordable and widely used, but they can cause foaming if added in excess.
• Polyquat Algaecides: A premium option that’s non-foaming and long-lasting—perfect for regular algae prevention.
• Natural Algaecides: Made from eco-friendly ingredients, these are great for those avoiding chemicals.

Why Use Algaecide?

Adding algaecide to your pool routine offers several key benefits:

• Prevents algae growth: Stops algae spores before they bloom.
• Enhances sanitizer performance: Works with chlorine or other sanitizers for optimal results.
• Maintains water clarity: Keeps your pool looking clean and inviting.
• Protects pool surfaces: Prevents algae buildup that can damage liners or tiles.

With the right algaecide dose and proper application, you can avoid common issues like cloudy water, pink slime, and white water mold and keep your pool crystal clear.

When to Use Algaecide for Maximum Effectiveness

Now that you are convinced about the necessity of adding algaecide to your pool, the next question on your mind has to be, “What is the best time to add algaecide to your pool?”

Preventative Use

Adding algaecide to your pool regularly helps stop algae before it starts. This is especially important during the warmer months when algae thrive. It is also the time when you can ill afford any algae growth to spoil the summer fun.

A small maintenance dose every 1-2 weeks can keep your water crystal clear. For even better results, combine it with proper water chemistry maintenance and regular brushing and cleaning of your pool.

After Treating Algae Blooms

If your pool water turns green, cloudy, or slimy, it’s time to act fast. The first step is, of course, to shock your pool to kill the algae. Depending on the severity you may have to repeat this process a few times.

Once you have got rid of the algae and your pool water is once again clear it is time to add algaecide. Algaecide will work with the chlorine to prevent the return of algae.

Typically, you may need a higher “outbreak” dose of algaecide after shocking to clear “algae bloom.”

Seasonal Maintenance

You need to add algaecide based on seasonal changes too.

• Before Pool Closing: When you’re winterizing a pool, use a special pool algaecide for winter to prevent algae from forming while your pool is covered.
• At Pool Opening: Once the cover comes off, and the pool water chemistry has been balanced, add algaecide to weaken any lingering algae spores and start the season with clear water.

High-Risk Situations

Certain conditions make algae more likely to grow, including:

• Heavy rains: Rainwater can introduce contaminants and dilute pool chemicals.
• Thunder Storms: High winds can blow algae spores, which are everywhere, into your pool.
• High phosphate levels: Runoff from fertilizers or debris can spike phosphates, a key algae food source. Use a phosphate remover to address this, along with a dose of algaecide.
• Increased pool use: More swimmers mean more contaminants, which increases the possibility of algae growth.

You need to add algaecide during these situations. Actually, I recommend adding algaecide even ahead of the high-risk situation, if you can anticipate it.

How Much Algaecide to Put in a Pool?

Determine Your Pool Volume

Before you can figure out how much algaecide to put in a pool, you need to know the volume of water in your pool. Here’s how to calculate it based on your pool’s shape:

• Rectangular Pool: Length × Width × Average Depth × 7.5 = Total Gallons
• Round Pool: Diameter × Diameter × Average Depth × 5.9 = Total Gallons
• Oval Pool: Length × Width × Average Depth × 6.7 = Total Gallons

You could also use my Free Pool Volume Calculator.

Dosage Chart for HTH Algaecides

Once you know your pool’s volume, use the dosage instructions on your pool algaecide packaging.

HTH is a well-known manufacturer of pool chemicals. They offer three algaecides. Here’s a summarized table comparing the three HTH algaecides:

Product	Ingredients	Design Use	Effectiveness
HTH 67089 Algae Guard Ultra	Proprietary blend for long-lasting protection	Heavy-duty algae control for all types	Long-lasting (up to 3 months) against all algae types
HTH 67084 Algae Guard Advanced	n-Alkyl dimethyl benzyl ammonium chlorides (9.96%)	All-in-one solution for regular maintenance	Fast-acting, effective against various algae types
HTH 67045 Algae Guard 10	Not specified, focuses on rapid action	Quick fix for green algae	Quickly kills green algae, less effective on others

The dosage for their products for every 10,000 gallons of pool water is as under:

	Dosage (fl. oz. per 10,000 gallons)	Dosage (fl. oz. per 10,000 gallons)	Dosage (fl. oz. per 10,000 gallons)
	Algae Guard Ultra	Algae Guard Advanced	Algae Guard 10
Initial Dose	16	4
Maintenance Dose	16	1	6.4
Mild Algae Dose	16
Severe Algae Dose	32

Factors Affecting Algaecide Dosage

Several factors can influence how much algaecide your pool needs:

1. Algae Type and Severity: Green algae may require a regular dose, while stubborn black algae or pink slime may need higher doses.
2. Water Chemistry: Keep your pH between 7.2 and 7.6 and ensure chlorine levels are balanced before adding algaecide. High alkalinity and pH levels make it easier for algae to flourish, requiring higher algaecide dosage.
3. Pool Usage: More frequent swimming will require more regular doses of pool algaecide.
4. Weather Conditions: Hot weather and heavy rains can deplete pool chemicals, increasing the need for algaecide.

Step-by-Step Procedure for Adding an Algaecide

Here’s a detailed step-by-step procedure for adding an algaecide to your pool, ensuring effective treatment and maintenance:

1. Test and Balance Pool Water

• Check pH Levels: Ensure the pH is between 7.2 and 7.6 for optimal effectiveness.
• Test Chlorine Levels: Make sure the free chlorine level is within the normal range (1-3 ppm). If it’s too high, wait until it drops to a safe level.

2. Prepare for Application

• Run the Pool Pump: Turn on your pool pump and filter. This helps circulate the algaecide evenly throughout the pool.
• Read Product Instructions: Carefully read the label on your specific HTH algaecide for dosage recommendations based on your pool size.

3. Add Algaecide

• Measure the Correct Dose: Use the dosage guidelines provided on the product label. For example:
  • For HTH Algae Guard 10, you might add approximately 2.6 fl oz per 1,000 gallons of water as an initial dose and follow up with maintenance doses every 3-5 days.
• Distribute Evenly: Pour the algaecide around the perimeter of the pool while walking along its edge to ensure even distribution.

4. Allow Circulation

• Keep Pump Running: Let the pump run for at least 24 hours after adding the algaecide to ensure thorough mixing and distribution.

5. Monitor Water Clarity

• After 24 hours, check the clarity of your pool water. If algae is still visible, consider brushing the walls and floor of the pool to remove any remaining algae.

6. Vacuum Pool

• Use a vacuum to remove any dead algae and debris from the bottom of the pool after treatment.

Pro Tip: Always shock first, then wait until chlorine levels return to normal before adding algaecide.

Troubleshooting Common Algaecide Issues

Even with proper use, problems can arise. Here’s how to handle them:

• Excessive Foaming:
  If foaming occurs, you’ve likely used too much quat-based algaecide. Use a pool clarifier to reduce foam.
• Staining:
  Copper-based algaecides can leave blue-green stains on surfaces. Keep pH and alkalinity levels balanced to prevent this.
• Ineffective Algae Control:
• Persistent algae might indicate imbalanced chlorine levels, poor filtration, or phosphate buildup. Use a phosphate remover alongside algaecide for stubborn algae.

Algaecide Safety and Storage

Handling Algaecide Safely

While algaecide is a helpful tool for pool maintenance, it’s still a chemical and must be handled carefully. Here are a few key precautions:

• Wear Protective Gear: Always wear gloves and eye protection when handling pool chemicals, including pool algaecide.
• Avoid Skin and Eye Contact: If algaecide comes into contact with your skin or eyes, rinse thoroughly with water and consult the product’s safety guide.
• Keep Away from Children and Pets: Store algaecide in a secure place to prevent accidental exposure.

Proper Storage of Algaecide

To maintain the effectiveness of your pool algaecide and ensure safety, follow these storage tips:

• Store in a Cool, Dry Place: Heat and moisture can degrade chemicals, so keep them in a shaded, well-ventilated area.
• Seal Tightly: Always close the container tightly after use to prevent spills or evaporation.
• Follow Manufacturer Instructions: Some algaecides may have specific storage requirements. Always refer to the label.
• Dispose Properly: If you need to discard unused algaecide, follow local guidelines for chemical disposal.

Thank you very much for reading the post. I do hope you found it informative and helpful.