Why Your Pool Water Looks Green But Clear: 4 Common Causes and How to Fix Them

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Why Does My Pool Water Look Green But Clear?

Is your pool water clear but has an annoying green tint? When pool water looks green but clear, one or more of the following may be going on:

1. Chlorine Levels are Too High, pH is down and corrosion is taking place
2. You have used Copper based Algaecides
3. Copper Compounds in Your Pool Water
4. Initial Stage of Algae Growth, algae is not floating in the water but just sticking to the pool walls & floor

Key Takeaways

• Green but clear water signals chemical imbalances or early algae growth.
• Test pool water for chlorine, pH, and metal levels regularly.
• High chlorine can oxidize metals, turning the water green.
• Copper algaecides or compounds often cause green tints.
• Early algae growth clings to walls and floors, not the water.
• Metal sequestrants and proper pH balance prevent discoloration.
• Regular cleaning and maintenance keep your pool crystal clear.

I must admit that the scenario of “pool water looks green but clear” is not the most common one for green pools, but it can happen.

Generally, when pools go green, the water gets cloudy too. This scenario is the most common one and it is possible to clear such green pools by shocking it.

However, when pool water looks green but clear, you need to test the pool water for several parameters and arrive at the course of action to be taken based on the test results.

Of course, it helps to know some pool water chemistry! Anyway, in this article I will walk you through 4 likely reasons for your pool water developing a green hue and the ways to fix each case.

Testing When Pool Water Looks Green But Clear

So, of course, before you can start turning your pool water that looks green but clear to a crystal clear blue color, you will need to test the pool water and determine the actual reason.

Typically, there are three test options available:

1. Test Strips
2. Chemical Test Kits
3. Electronic Test Kits

Most home pool owners use test strips and some may use chemical test kits. The trouble is that these do not measure metal levels in the pool.

Of course, you do not have to invest in some high priced, fancy, water testing equipment. Your friendly pool chemicals supplier can do it for you.

So let me explain each specific reason and the best fix for it!

1. High Chlorine Levels

It might seem surprising, but too much chlorine in your pool can cause the water to appear green. This occurs because excessive chlorine can lower the pool’s pH, making the water more acidic and potentially corrosive.

When this happens, metals in the water or on pool equipment, such as filters, pumps, vacuums, or ladders, oxidize. The metal oxides, particularly copper or iron, are often green and can create a greenish tint in the water.

To prevent this, test regularly and maintain your pool’s chlorine levels within the recommended range (1-3 ppm).

If the free chlorine level is too high, follow these steps to bring it back into balance.

How to Fix High Chlorine Level

1. Test Your Pool Water
   • Use a reliable pool water testing kit to check the chlorine levels.
   • Record the chlorine level to determine how much adjustment is needed.
2. Stop Adding Chlorine
   • Immediately discontinue adding chlorine or chlorine-based products to the pool.
3. Dilute the Pool Water
   • If chlorine levels are only slightly high, partially drain the pool and refill it with fresh water.
   • Retest after dilution to ensure the chlorine level has decreased.
4. Use a Chlorine Neutralizer
   • If the chlorine level is excessively high, add a chlorine neutralizer (e.g., sodium thiosulfate) to the pool water.
   • Follow the product’s instructions carefully to avoid reducing the chlorine level too much.
5. Expose the Pool to Sunlight
   • Chlorine naturally dissipates when exposed to sunlight.
   • Remove the pool cover, if applicable, and allow the pool to remain uncovered for several hours.
6. Increase Pool Usage
   • Encourage swimming and other pool activities, as chlorine levels decrease with use.
7. Maintain Proper Water Balance
   • Once chlorine levels are back to the recommended range, test the pH and alkalinity.
   • Adjust pH to a range of 7.2-7.8 and total alkalinity to 80-120 ppm to keep the pool water balanced and prevent further issues.
8. Regular Monitoring and Maintenance
   • Test your pool water regularly to ensure chlorine levels stay within the optimal range.
   • Consider investing in an automatic chlorinator or pool monitoring system for consistent results.

2. Copper-Based Algaecides

Copper-based algaecides are commonly used to prevent and control algae growth in swimming pools. However, these algaecides often cause the water to appear green but remain clear.

Copper in the algaecide reacts with chlorine in the pool, forming cuprous chloride, which gives the water a greenish tint without making it cloudy.

Using a higher-than-recommended dose of copper-based algaecide can exacerbate the problem. Fortunately, you can restore your pool’s crystal-clear blue color by following a few simple steps.

How to Fix Green Water from Copper Algaecides

1. Test Your Pool Water
   • Use a pool water testing kit to check copper levels.
   • In case you do not have the required testing kit, you can take a sample of the pool water to your pool chemical supplier. They can test it for you and tell you the copper content in it.
   • Note if the copper levels exceed 0.2 ppm, as this is typically when discoloration occurs.
2. Switch to a Metal-Free Algaecide
   • Replace your current copper-based algaecide with a non-metallic, non-staining alternative like ProTeam Polyquat 60.
   • ProTeam Polyquat 60 is an algae preventative for hard-to-kill mustard, black, and blue-green algae types. This product is non-metallic and non-staining.
   • It also reduces sanitizer consumption and is not affected by high chlorine residuals.
3. Partially Drain and Refill the Pool(if copper levels are high)
   • If the copper levels in your pool are significantly high, partially drain the pool and refill it with fresh water.
   • This helps dilute the copper concentration and minimizes the green tint.
4. Use a Metal Sequestering Agent
   • Add a metal sequestrant to your pool water to bind with the copper, preventing it from reacting with chlorine.
   • Recommended Metal Sequestering Agent
     Pool Mate Metal Out Stain and Mineral Inhibitor
     Prevents discoloration of pool water due to iron, calcium, manganese, copper, and other metals and minerals.
5. Shock the Pool (Carefully)
   • If necessary, shock the pool to remove any residual organic material.
   • Avoid using a shock treatment that contains additional metals, as this may worsen the issue.
6. Brush and Vacuum the Pool
   • Thoroughly brush and vacuum the pool to remove any algae, dirt, or debris that may exacerbate the discoloration.
7. Monitor pH and Chlorine Levels
   • Regularly test and adjust the pool’s pH and chlorine levels to keep them within the recommended range:
     • pH: 7.2-7.8
     • Free chlorine: 1-3 ppm
   • Proper water balance prevents unwanted chemical reactions.

3. Copper Compounds in Pool Water

Copper compounds in pool water can cause the water to appear green but remain clear, even when chlorine levels are within the recommended range. This green tint occurs when chlorine reacts with copper, forming cupric chloride.

Copper compounds can enter your pool in several ways:

1. Water Supply: Well water or municipal water often contains trace metals like copper.
2. Rainwater and Storm Runoff: Rain and floodwaters can introduce metals and debris into the pool.
3. Pool Chemicals and Equipment: Some pool chemicals and equipment contain metallic components that can leach into the water, especially in unbalanced conditions.
4. Pool Heater: A corroding copper heat exchanger can release copper into the water due to poor chemical balance.
5. Accidental Sources: Items like hair clips or non-pool toys can inadvertently introduce metals.
6. Fertilizers: Lawn or garden fertilizers may wash into the pool, carrying heavy metals like copper, iron, or manganese.

Fortunately, there are effective ways to remove copper compounds and restore your pool’s clarity.

How to Remove Copper Compounds

1. Test Your Pool Water for Metals
   • Use a pool testing kit designed to detect metal levels, particularly copper.
   • In case you do not have the required testing kit, you can take a sample of the pool water to your pool chemical supplier. They can test it for you and tell you the copper content in it.
   • Note any levels above 0.2 ppm, as this can lead to discoloration.
2. Add a Metal Sequestering Agent
   • Use a product like Pool Mate Metal Out (mentioned under section 2) to bind with the copper and other metals, preventing them from reacting with chlorine.
   • Follow the manufacturer’s instructions for dosage based on your pool size and metal levels.
3. Balance Pool Chemistry
   • Ensure your pool’s pH, alkalinity, and calcium hardness are within the recommended ranges to prevent corrosion of metal components:
     • pH: 7.2-7.8
     • Total alkalinity: 80-120 ppm
     • Calcium hardness: 200-400 ppm
   • Proper balance reduces the risk of metals dissolving into the water.
4. Dilute Metal Levels with Fresh Water(if needed)
   • Partially drain and refill the pool with fresh, metal-free water if copper levels remain high.
   • Test the water after dilution to confirm improvement.
5. Clean the Pool Thoroughly
   • Brush the pool walls and vacuum the bottom to remove debris that could introduce or hold onto metals.
6. Install a Metal-Removing Filter(optional)
   • Consider using a specialized filter to remove metals from your pool water.
   • This can be especially helpful for pools using well water or located in areas with high natural metal content.
7. Monitor for Future Metal Contamination
   • Test the water regularly to detect rising metal levels early.
   • Avoid using metal-based algaecides or fertilizers near the pool area.
8. Protect Against Metal Buildup
   • For pools in areas with metal-rich water sources, use a product like Pool Mate Metal Out regularly as a preventative measure.
   • This helps control general stains and maintains a sparkling clean pool.

4. Initial Stage of Algae Growth

When your pool water looks green but clear, it could be due to the early stages of algae growth. At this point, the algae are microscopic and cling to pool walls and the floor, rather than floating freely in the water.

This can occur when free chlorine levels are too low to properly sanitize the pool.

If left untreated, the algae will multiply and cause the water to turn cloudy and visibly green. Consider this green tint as a warning sign and act promptly to prevent a full-blown algae bloom.

How to Treat Early Algae Growth

1. Test Your Pool Water
   • Use a pool testing kit to check the following:
     • Free chlorine levels (should be 1-3 ppm).
     • Combined chlorine levels (should be less than 0.5 ppm).
     • pH levels (should be between 7.2-7.8).
   • If free chlorine is low or combined chlorine is high, it’s time to take corrective action.
2. Shock the Pool(Superchlorinate)
   • Raise the free chlorine level to 10 times the combined chlorine level (commonly known as the breakpoint chlorination threshold). You can use my pool shock calculator to determine the dose!
   • Follow these steps for effective shocking:
     • Dissolve the shock treatment in water before adding it to the pool to prevent bleaching pool surfaces.
     • Add the solution to the pool in the evening or at night to minimize chlorine degradation from sunlight.
     • Run the pool pump continuously for 24 hours to circulate the chlorine evenly.
3. Brush Pool Walls and Floor
   • After shocking the pool, thoroughly brush the walls and floor to loosen algae clinging to the surfaces.
   • Use a brush suitable for your pool type (e.g., nylon brushes for vinyl and fiberglass, stainless steel brushes for concrete).
4. Vacuum Dead Algae and Debris
   • After brushing, dead algae may settle on the pool floor. Use a pool vacuum to remove the debris.
   • Consider using a flocculant to clump together fine particles, making it easier to vacuum.
5. Balance Pool Chemistry
   • Retest the water and adjust pH, alkalinity, and chlorine levels to maintain a healthy balance:
     • pH: 7.2-7.8
     • Free chlorine: 1-3 ppm
     • Total alkalinity: 80-120 ppm
6. Prevent Future Algae Growth
   • Maintain proper sanitation by ensuring chlorine levels stay within the recommended range.
   • Regularly clean and brush your pool, especially after storms or heavy use.
   • Run the pump and filter for at least 8 hours a day to improve circulation.
   • Use an algaecide as a preventative measure, choosing a non-metallic option to avoid discoloration.

By addressing algae growth in its early stages, you can restore your pool’s sparkling blue clarity and prevent the green tint from worsening.

Keep your pool sanitized and properly maintained to enjoy algae-free swimming year-round.

Frequently Asked Questions (FAQs)

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