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After following our blog "What is causing my algae and what can I do about it?" you are now ready to get some algaecide. There are so many algaecides on the market though that it’s hard to know which one to choose. Many pool owners rely on anecdotal advice from others, or they "judge the book by its cover" and pick the product with the flashiest label or ad. Even worse, some take advice from a pool store clerk who has no formal training and is more interested in selling chemicals than solving your algae problem.

In this post, I’ll break down the different types of algaecides—highlighting which ones to avoid, which require special care, and which actually work. We’ll focus primarily on yellow algae (also known as mustard algae), the most common algae found in pools.

📌 A Quick Note: Despite the name, yellow algae often appears green in your pool due to the water’s natural blue tint.

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🧪 Types of Algaecides (By Active Ingredient)

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Algaecides are typically categorized by their active ingredients, including:

• Copper

• Silver

• Sodium Bromide

• Ammonium Sulfate

• Ammonium Chloride (includes quats and polyquats)

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📌 Tip: You can find the active ingredient near the bottom of the front label, usually listed with percentage concentrations.

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🥇 Copper-Based Algaecides

✅ Most Effective For Yellow Algae| ⚠️ Requires Careful Use

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Copper algaecides are widely considered the most effective option. However, they come with a few important caveats:

Pros:

• Highly effective against yellow, green, and even black algae

Cons:

• Staining can occur, especially with cheaper products that lack proper chelating agents

• Heavy metal toxicity is a concern if not used properly

🔬 How to use it safely:

• Always test total iron and copper levels (not just free copper) before use.

• If levels are too high, lower them before applying copper-based products.

💡 After decades of experience, I now use only copper-based algaecides to treat yellow algae in my professional service—with consistent results.

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🥈 Silver-Based Algaecides

✅ Best for Black "Algae" (Cyanobacteria)

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Silver is more effective against bacteria than algae, making it a strong choice for black algae—which is actually a type of cyanobacteria.

Important Notes:

• Can cause black or gray staining on tiles or surfaces if not cleaned beforehand

• Like copper, silver levels should be tested before use

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🚫 Sodium Bromide

❌ Just Say No

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Avoid sodium bromide entirely. It transforms your chlorine pool into a bromine pool, and the only way to reverse this is by draining the water.

Why this is a problem:

• Bromine is “activated” by chlorine but cannot be stabilized like chlorine

• In hot weather, chlorine might lose 1 ppm per day, while bromine can lose 1 ppm in just 4 hours

• Many pool owners don’t properly shock the pool (10+ ppm chlorine), leading to ineffective treatment and algae returning stronger

📌 Advice: Avoid any product that contains sodium bromide or other bromine compounds.

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⚠️ Ammonium Sulfate

🚫 Temporary Fix, Long-Term Headache

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While ammonium sulfate may appear effective if used exactly as directed, it creates bigger problems over time.

Why it’s problematic:

• Produces monochloramines, which are less effective than free chlorine that you would get if just "shocking" or super-chlorinating alone

• Requires "shocking" to work

• Leaves behind nitrogen, which turns into nitrates, a food source for algae

🔥 Analogy: Using ammonium sulfate is like putting out a fire with gasoline. It might suppress the flame from a match, but would you use it to put out a house fire?

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⚖️ Quaternary & Polyquat Algaecides

🛡️ Preventative, Not a Cure

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These are algaestats, not algaecides—meaning they help prevent algae growth but don't reliably kill existing algae.

Key Differences:

• Quaternary algaecides often cause foaming

• Polyquats are non-foaming and more stable

Best Practice:

• Let the algaestat work for 24 hours, then follow up with a chlorine shock

• Be aware: Like other ammonium-based products, they break down over time and leave behind nitrogen

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💊 PoolRX

💰 Same as Copper, but EXPENSIVE

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Copper (or Copper + Silver) in a Unique Delivery System

PoolRX is a popular product with a unique design, but at its core, it's still a copper algaecide. The PoolRX Plus version also includes silver.

📌 Click Here to read more about PoolRX.

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🌿 Phosphate Removers

✅ Not an Algaecide—but Still Powerful

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Phosphates are algae’s primary food source. Remove phosphates, and you effectively starve the algae.

Pros:

• Highly effective immediately killing existing algae and for long-term prevention

• Non-toxic and safe to use

Cons:

• More expensive than traditional algaecides (but well worth it)

• Can temporarily make the pool cloudy

💡 For ongoing maintenance, phosphate removal is a smart investment.

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🤔 Final Thoughts

Your best defense against algae isn’t just the right bottle—it’s ongoing, informed pool care.

If you're in the Temecula Valley, consider working with a trusted, experienced team like POOL NERDS. We maintain balanced chemistry, regularly test for metals, keep phosphates in check, and use only the most effective, safest treatments available.

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👉 CLICK HERE to read more about choosing the right pool service company.