If you are reading this, unfortunately, you may already know what rust stains look like. But if not, then what you are looking for is dark red or rusty in color. They can be small spots or they can cover sections of a pool, both on the walls, floor, and steps.
What Do Rust Stains Look Like?
Here are some pictures of pools with rust stains on them. Notice they are a dark red, brownie rusty color. They are often found near fittings such as lights, pool drains and ladders.
Are Brown Stains Iron or Rust Stains?
Iron is what causes rust staining, and using the color brown can be a little confusing as brown stains can also be caused by organic materials such as leaves or acorns.
If there is iron in the pool water, then high chlorine and pH above 7.4 can cause the iron to fall out of the solution and deposit on your pool walls and floor as ugly brown stains (rust).
Additionally, if objects made of iron such as screws or hair pens are allowed to sit on a pool surface, then the pool water will eventually oxidize them and you will end up with rust spots in the shape of those objects.
How to Tell if You Have a Rust Stain
If you have a dark spot that you think is iron staining then you can either purchase a stain test kit or use the home remedy test of placing plain vitamin c tablets on the stain to see if they lift it. If the tablet doesn’t lift it then you are looking at an organic stain and chlorine will likely be your answer for removal.
- One way to distinguish between iron and organic stains is that rust stains are more of a brownish-black color and organic stains are more of a brownish-green color.
- If the brown stain is in the shape of a leaf then, you guessed it, it’s caused by a leaf.
- If the stain is on the wall of the pool then it’s most likely not from a leaf or other organic matter since they typically do not stick to the side of the pool and will sink to the bottom.
Are Iron or Rust Stains Bad?
I don’t know about you, but I consider any stain to be bad. Not in the sense that it can do physical harm or is dangerous to swimmers, but that it leaves unsightly stains in your beautiful pool.
What Causes Iron (Rust) Stains in Pools
Rust stains can be caused by several different things, but they all have one thing in common – they involve iron. Let’s have a look at how iron can stain.
- Objects such as nails, hairpins, or screws are allowed to sit on the pool surface.
- Toys that are not made for pools and contain iron parts can also stain.
- Lawn fertilizer that makes its way into the water from over broadcasting contains iron additives.
- Rust in pipes that feed the pool freshwater.
- Fill water that comes from a well can contain iron and other metals.
- Rebar used in the construction of concrete pools that is too close to the surface or exposed to water will rust through the plaster.
- Pool fixtures such as metal ladders, pool lights, pool drains, and the screws used to fix these items to the pool can rust and stain a pool.
Rust stains can be removed from the pool surface by using an acid product or a stain remover product. You do want to pay particular attention to what type of pool surface you have because some methods can damage your pool. We will cover this in more detail below including recommending some products.
There are several methods that can be used to remove rust stains from pools and they vary based on the type of pool surface and the extent of staining. The fix could be as simple as using vitamin c tablets to remove small spot staining or as complex as draining the pool and acid washing with a dilute concentration of muriatic acid.
Let’s Jump In and Have a Look at Some Ways to Get Rid of those Ugly Iron Stains.
Here’s a quick summary of the different methods available and what they’re best for.
|Rust Stain Removal Method||Pool Type||Best for Stain Type|
|Vitamin C tablets (Ascorbic Acid)||Plaster, Vinyl, and Fiberglass Pools||Small rust stains are caused by metal objects in the pool such as hairpins.|
|Stain Eraser Tool|
|Ascorbic Acid Powder||Plaster, Vinyl, and Fiberglass pools.||Multiple or larger stains. Use when there are too many stains use Vitamin C tablets.|
|Muriatic (Hydrochloric) Acid||Plaster pools||Small and large stains that are unable to be removed using vitamin C or ascorbic acid powder.|
1. Use Vitamin C (Ascorbic Acid)
Suitable for: Plaster, Vinyl, and Fiberglass Pools
Vitamin C contains ascorbic acid and is an easy way to handle small stains such as those caused by metal objects falling in the water or fertilizer being over broadcast in the pool.
OK, now that you know I have damaged my own plaster before, let’s look at how to spot and treat a few rust stains.
- Add about 15 to 20 vitamin c tables to an old sock and place the sock on the stain.
- Leave the sock for a minute or rub the stain with it and then brush to remove the stain.
- If it isn’t gone, reapply the sock for another minute and repeat rubbing and bruising.
- Do this until the stain is totally removed and be sure to do a final brush of the area to disperse the vitamin c as it’s acidic.
- Don’t worry about the iron ions redepositing as long as you have less than 0.2 ppm iron content in the water. The amount of iron from small stains such as a hairpin or a screw isn’t enough to redeposit into a stain once lifted.
- Put the tablets in a zip lock bag and crush them to make a powder.
- Sprinkle the powder over the stained area and let it sit for about 2 minutes before brushing.
- If the area is medium-sized and you need more than a couple of bottles on tablets it may be more economical to buy ascorbic acid powder or a stain removal product containing ascorbic acid. See below.
2. Stain Eraser Tool
Suitable for: Plaster and Fiberglass pools.
For smaller stains, you can use a tool called the Stain Eraser. You simply rub the stain with the eraser and keep rubbing until the stain is gone. For stains that are too deep to reach you can attach the eraser to your pool pole, but be patient because it’s hard to put enough pressure due to the leverage and it may take longer to remove the stains.
3. Ascorbic Acid Powder
Suitable for: Plaster, Vinyl, and Fiberglass pools.
Sometimes there are too many stains or there is an area that’s too large to spot treat with a sock. If you have that issue then the best resolution is to use ascorbic acid powder or if you are treating a vinyl liner pool then use a product such as The Vinyl Liner Blue Stuff by Jack’s Magic to treat the stains.
This is a bit more involved, but it will cover a much larger area and is a good DIY method.
Steps for Using Ascorbic Acid
1. Lower your chlorine to 0 and pH to 7.2, if there is chlorine in the water it won’t hurt, it will just eat up the ascorbic acid, so you will need more to get rid of the stains.
2. If you think you may get algae you can add Polyquat 60, but do not use a copper-based algaecide.
3. You will need about a half to one pound of ascorbic acid per 10,000 gallons, and it’s best to gradually increase the amount until the stains are gone.
4. Add the acid around the perimeter of the pool and set your filter to RECIRCULATE, or if you have a cartridge filter then you can just remove the cartridges and let the water circulate.
5. Brush the pool to stir the acid.
6. Run your pump for about 2 hours.
7. If the stain hasn’t disappeared, add more acid or let the pump run longer. You can also brush stubborn areas to help the acid penetrate the stain.
8. After the stain has been removed, add a sequestering agent per manufacturer directions for your pool volume to keep the metal from redepositing.
9. Return the filter to “filtration mode,” or put your cartridge filters back in, and let the pump run for 24 hours.
10. If you see stains forming again when you start raising your chlorine, make sure the pH is 7.2 and add some more sequestering agent.
11. Your water will likely be cloudy, but it will clear with time as long as you leave the pump running 24×7.
12. Add CuLator according to the manufacturer’s instructions for your pool volume in order to fully remove the metal ions as the sequestering agent disappears over the next 30 days. Alternatively, you can also drain and replace some of the pool water. This will dilute the metal content.
4. Muriatic (Hydrochloric) Acid
Suitable for: Plaster pools.
Muriatic acid is a great way to remove iron stains, but it can also stain decks if spilled and it can ruin pool surfaces if used in too high of a concentration. Remember to always wear protective gloves and eyewear when handling acid to avoid personal injury.
One word of caution here, there are many sites and social media posts that recommend pouring muriatic acid down a PVC pipe that’s positioned directly over the rust stain – DON’T DO THAT unless you are experienced with this method.
Trust me from experience, if you don’t know what you are doing you will erode your pool plaster.
Now that we have covered the safety precautions and hazards, let’s look at how to safely use muriatic acid for removing stains.
Note that muriatic acid can be used for both small stains and large or pervasive staining.
Steps for Using Muriatic Acid
For Small Stains:
- Dilute the acid 2 parts water to 1 part acid, to begin with and if the stain isn’t coming up then you can move from one part acid to one part water. Remember to always “add acid” to water and not the other way around as adding water to acid causes a violent reaction.
- Carefully pour the solution at the end of the pipe and then brush with a pool brush to distribute the acid and lift the stain. If it doesn’t come up at first, try more acid and/or increase the concentration.
Tip: There are tools such as the Purity Pool Stain Remover that are self-contained and make the application of acid (both liquid and powder) much easier, and frankly work better than the PVC pipe and brush method.
For Large Stains:
Acid washing is the best way to remove larger stains that cover the entire pool and/or multiple walls. It is more invasive and harsher on the plaster, but it is quite effective.
There are 2 ways to acid wash, a no-drain method, and a full drain method. It’s our experience that the full drain method works better and removes more staining, but it is more work and may not be an option in some regions.
Steps for No-Drain Acid Washing
- Make sure that you have at least 3 days to commit to closely monitoring your chemistry and brushing the pool. It’s preferable to do the treatment when the water temperature is below 60F in order to avoid algae growth.
- About a week before you start the process, clean the pool well and make sure you do not have any algae. You may need to shock to be sure.
- Add a sequestering agent 2 days prior to starting, and add polyquat algaecide 1 day prior to starting.
- Turn off your pump (and close the valves to your heater if you have them to keep from accidentally damaging the heater coils with the acidic water.
- Remove any objects such as pool cleaners, light rings, and ladders to prevent them from being damaged by the acidic water.
- Add enough muriatic acid (or sodium bisulfate) to drop the alkalinity to zero, (pH will be in the range of 4). Brush the pool to mix.
- Brush the pool several times per day with a steel pool brush, paying attention to the stains.
- Test the water daily to make sure your pH and alkalinity are still low as this is the key to lifting the stain.
- After the stains begin to lift and get lighter, begin to raise the pH and Alkalinity with Soda Ash to stop the process.
- Add soda ash (pH increaser) in 3 separate doses and about 7 hours apart to help avoid cloudiness. Be sure to brush well after each dose.
- Once your pH is above 7.2 you can open the valves to your heater and restart your pump.
- Replace any items you removed.
Steps for a Full Drain Acid Wash
Caution should be used when attempting to acid wash a pool. If done incorrectly, you will be left with a rough pool surface. Consult a professional if you have any concerns.
- Drain the pool water using a submersible pump. You may be able to use your main drain and pool pump if you have valves to turn off your skimmer suction.
- Wear appropriate safety gear (rubber boots, gloves, eyewear, respirator.)
- Make a mixture of muriatic acid and water, 3 parts acid to 7 parts water.
- Use a water hose to wet the floor.
- Use a garden water can to pour the acid mixture from the shallow end and work your way along the floor to the deep end.
- Rinse off the acid 15-20 seconds after it is first applied by brushing and hosing at the same time.
- Once the floor is complete then wet the walls of the pool and pour your acid mixture starting at the top using the same method as the floor.
- Work in a pattern all the way around the pool and do not stop until you have completed it all or you risk an uneven finish.
- Use soda ash to neutralize the acid, 2 pounds of soda ash for every gallon of acid applied to the surface. Be sure to keep count to keep the wastewater puddle neutral or it can stain the floor.
- Refill your pool and balance the water.
- Be careful that you determine where the metal stains came from so that you don’t reintroduce them in the future.
How to Remove Metals and Iron From Pool Water
As you now know, you have rust and iron stains in your pool because you either have high amounts of metals and iron in the water or metal objects in the water have rusted.
The best way to prevent staining due to iron in the water is to remove metals from your water or bind them chemically so that they can’t precipitate onto the surface. Metal can also be removed by filtering it out, however, that’s not always effective and depends on the type and quality of filter used.
We have a full article on iron removal here: How to Remove Iron from Pool Water (Water High with Iron)
Here’s a quick summary of the products available for iron and metal removal…
Products for Iron and Metal Removal (Prevention of Stains)
Each product has its own benefits, but no matter which you choose it’s best to completely remove the metal ions with CuLator to be sure that you are eliminating the risk of staining.
Note that these products aren’t meant for stain removal, they are meant for removing or binding metal in your water before it stains.
Sequestering/chelating agents can be used in conjunction with large stain removal so that as the ions are freed up they are bound by the agents and can’t redeposit. We also recommend using CuLator in conjunction in order to completely remove the metal.
|Chelating Agent||Sequestering Agent||CuLator (Polymer Binding agent)|
|How the agent works||One-to-one bonding of ions. |
Binds to metal ions to prevent them from undergoing chemical reactions such as oxidation which causes staining.
|Many too many bonding of ions forms a larger complex molecule that can be filtered out.||Bonds with metal ions and traps them for complete removal.|
|When to use||New pool startups to prevent staining|
Trace level of metals
|New pool startups to prevent staining|
Well water fills or refills
Higher level of metal content
|New pool startups to prevent staining|
Clearwater from oxidized copper-based algaecide and oxidized iron
Well water fills or refills
Higher level of metal content
|Pros||Easy to use|
Quick treatment for preventing staining without waiting for total removal
|Easy to use|
Quick treatment to prevent staining without waiting for total removal
|Completely removes metal ions|
|Cons||Does not remove metal ions|
Requires weekly maintenance doses
|Does not remove metal ions|
Requires weekly maintenance doses
|Can take time to fully remove metal ions|
Tips to Prevent Iron Stains
- If your fill water has iron in it, then consider having water delivered by truck for your initial fill.
- Do not use toys that aren’t designed for use in the pool. Especially toys that may contain batteries.
- Check the pool after swimming or parties to make sure everything has been removed and look closely for small objects such as hairpins or other metal objects.
- Use your vacuum to clean the floor after parties to suck up anything that doesn’t belong.
- Do not use broadcast spreaders for lawn fertilizer near the pool.
- Consider using sequestering agents and/or filters if your fill water contains metal
- Do not use copper-based algaecide as it adds copper to your water. You can instead use polyquat algaecides.