How you remove metal stains from your pool depends on the extent of the stain, where it’s located in the pool and the type of pool surface.
First of all before you can remove a stain you need to identify what caused the stain. Not all pool stains are caused by dissolved metal ions in the water. Many stains are simply caused by decomposing organic material such as insects, flowers, leaves, seeds and berries that have sunk to the bottom. These organic stains are usually green or brown in appearance.
Other stains can be the beginning of green or black algae growing in the pool.
Metal stains are caused by higher than normal concentrations of soluble metal ions in the water. Metal stains are usually darker colors of green, blue, brown, purple or black in appearance.
Whatever the reason for your pool stains you need to act fast to remove them from the pool and prevent them from recurring.
Table of Contents
What are Metal Stains in a Pool?
Different stains require different type of treatment.
Before you try to clean metal stains from a pool or spa you need to identify the type of stain and what causes it.
Metal stains are caused by excessive metal ions in the pool water.
Pool Chemistry Lesson: When an atom (or group of atoms) gains or losses one or more electrons it becomes a charged particle, called an ion.
Blue, Green, Black stains indicates copper ions.
Brown, Green, Red stains indicates iron ions.
Dark Purple, Dark Brown, Black stains indicates manganese ions.
Organic stains can be deposited by leaves, flowers, seeds and other organic material when they decompose on the bottom of the pool.
Green & brown stains are insects, leaves, flowers or seeds.
Red or blue stains are berries and flowers.
How Do Metal Ions Get in the Pool?
Water Source
If you filled the pool with a water source other than your town water supply you may have introduced metal ions into the pool. Water from bores, dams, streams, rainwater tanks and other sources may contain high levels of metals. These metals will raise your total dissolved solids (TDS) level and may cause problems sanitizing and balancing the water chemistry.
Metal Pipe Corrosion
Copper or iron may have come from a corrosive water pipe or metal fitting in the water heater or filtration system. Normally mains water pipes are well maintained and cause no problems. Councils have to provide drinking water with total dissolved solids (TDS) less than 500 ppm so there shouldn’t be any metal ions in your drinking water.
Algaecide Chemicals
Some brands of algaecide contain copper ions. Too much use of these algaecides over time can add copper to the pool increasing the TDS.
What Causes Metal Stains to form in a Pool?
When your pool water has higher than normal concentrations of soluble metal ions changes to the pool chemistry will cause the ions to react with the pool surface causing staining. This occurs with high pH and high total alkalinity levels.
Equipment such as ladders, rails, pool lights and any other metal fittings can become stained and accumulate calcium scale.
How to Remove Organic Stains from a Pool
Many organic stains, which are caused by decomposing leaves, flowers and seeds, can be successfully treated with chlorine.
Algae is another source of stains and marks in pool.
If you think you have algae in your pool, read our article on How to Get Rid of Algae in Your Pool
Wear gloves and eye protection when handling liquid chlorine.
Apply some liquid chlorine to a sponge and directly rub the stain. The sponge can be attached to a telescoping pool pole to reach to the bottom of the pool.
Let the chlorine soak into the stain for a while then brush away the stain.
When there are multiple stains around the pool super chlorinate the pool. You will need to double or triple shock the pool to have any effect on organic stains. Always add shock in the evening so the chemicals have all night to work without being effected by the sun.
After adding the shock ensure the pump is running for at least 4 hours to circulate the chemical around the pool.
Brush the stains frequently to remove them from the pool.
Read our detailed article on How to Shock Treatment Your Swimming Pool
How to Prevent Organic Stains in a Pool
Preventing organic stains from forming in your pool is easy.
- Keep the correct level of sanitizer (chlorine, bromine, etc.) to kill bacteria and algae before it can multiply in the pool.
- Ensure the water chemistry (especially pH and total alkalinity) are in the normal ranges all the time.
- Use a pool cover to keep organic material out of your pool.
- Use a skim net to remove organic material floating in the pool before it sinks to the bottom and decomposes.
- Run your pump long enough each day to remove organic matter from the surface and trap it in the skimmer basket.
- Regularly vacuum the bottom of the pool to remove sunken organic material.
- Install an automatic pool cleaner to keep the bottom free of organic material.
How to Remove Metal Stains from a Pool
The method to remove metal stains depends on the extent of the stains in the pool. If there are few stains in number try to treat each stain separately. If the whole pool is full of stains then clean metal stains from a pool by treating the pool water.
Once you have identified the type of stain and its source you can attempt to clean metal stains from a pool. Many metal stains can be chemically treated in the pool water while other more difficult stains may require draining the pool.
Without Draining the Pool
Choose only one of the following methods to remove metal stains from your pool. Do not use all methods together.
Shock Treatment
Add shock to the pool water to oxidize the metal ions into harmless molecules that will sink to the bottom where they can be picked up by the pool cleaner or manually vacuumed away. You may require several shock treatments over a period of weeks to oxidize enough metal from the water. Also you may need to double or triple the dosage of shock to oxidize the metals out of the water.
This method may take many days or weeks to clean up the pool and eliminate the metal stains.
Sequestering Agent
Add a metal sequestering or chelating agent to the pool. These chemicals form complex metal molecules that sink to the bottom where they can be vacuumed away. This method may take a week to see positive results.
Citrus-Based Stain Remover
This method works the fastest but will throw out the balance of your pool chemistry which will need to be re-balanced at the end of the process.
Swimming pool water should normally be between pH 7.2 and 7.8 which is slightly alkaline and never acidic.
Lower the pool’s pH to 7.2 which is the low end of the normal pH range. This is necessary to ensure the citrus or ascorbic acid works at removing the stains.
Use muriatic or hydrochloric acid to lower the pH.
Read our article on How to Lower pH in a Swimming Pool for more information.
Apply a citrus-based stain remover directly to the stain and water around the stain. Read the instructions on the container. Usually it is best to pour the stain remover around the edge of the pool so that it reaches the sides and corners at the bottom. Activate the pump and circulate the water around the pool. The stains should fade away in about 30 minutes.
Rub a tough stain directly with a vitamin C tablet. The ascorbic acid (vitamin C) can also help remove the stain.
Keep the filter on for at least 3 or 4 hours to circulate and remove contaminants from the water.
Re-balance the pool water the next day.
Read our article on How to Balance Your Pool Water
Drain the Pool to Remove Metal Stains
Swimming pool water accumulates contaminants, metals and other dissolved solids over time which cannot be chemically removed from the water. When the total dissolved solids in the water are higher than 6000ppm it’s time to empty the pool.
Replace your pool water should every 5 years to combat this problem. While the pool is empty take the opportunity to remove scale, stains, make repairs or renovate the pool surface.
How to Prevent Metal Stains in a Pool
- Always maintain your pool chemistry and test the water every week.
- Avoid filling the pool with water containing metal ions. Always test the water source first for metals. Do not use water from bores, streams and dams. Rainwater captured from your roof is usually ok but have it tested to make sure.
- Drain and refill your pool water every 5 years to eliminate total dissolved solids.
- Add a metal sequestering chemical to the water to prevent the staining problem recurring.
- Check your water heater for metal corrosion which will leach copper and iron into the pool water. Also check for accumulated calcium scale in the heater.
- Check your filtration system for metal parts that are showing signs of corrosion. Most systems are manufactured with PVC plumbing which cannot corrode but there may be a small metal part that has corroded. If so replace it with a new fitting.
- Check your chlorinator cell for corrosion on the electrodes. Acid wash your chlorinator cell to remove corrosion and scale.
Conclusion
Maintain correctly balanced pool water to avoid metal stains forming in your pool.
Test your pool water every week and take action as soon as the water becomes unbalanced.
Once metal stains have formed in your pool re-balance the pool water chemistry and remove the stains with the above methods.
Add a metal sequestering chemical to the water to prevent the staining problem recurring.