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What Causes Rust Stains in Pools and How Can They be Remedied?

Over time, pool owners may encounter a number of curiously colored stains on the surface of their pool. Some of the most commonly colored stains they’ll notice are dark red and rusty brown, which while alarming at first, may not necessarily indicate that something is seriously wrong with your pool. But how do you know when it’s cause for concern?

The Most Common Cause of Pool Staining

There are a number of reasons why you’ll see staining throughout your pool. Below are just a few of the most common reasons why you may be noticing rust stains in pools. 

Organic Materials

Organic decaying debris like leaves, twigs, pine cones and acorns sitting on the surface of the pool can result in rust-colored stains. Typically these materials will leave an impression which resembles the shape of the stain-producing product (such as the outline of a leaf).

Metal Objects

Anything from bobby pins to toy cars to nails can cause rust to appear in your pool. These objects should be removed as soon as they are discovered. This is particularly true if you have very acidic pool water, as the more acidic your pool, the greater the problem you’ll have.

Metal in the Water

Also known as the oxidation of water, if you are regularly seeing small rusty spots in your pool it may be because your water contains small metal fragments. Iron in your pool water is especially problematic, and it can quickly lead to costly repairs.

Rebar Stains

Rebar are the metal shafts found beneath the plaster of your pool. Left untreated, the rebar will eventually cause the shell of your pool to crack. This will expose more rebar which will lead to further corrosion until your swimming pool is no longer structurally sound.

Rebar stains are often the result of there not being enough coverage provided around the reinforcements. When rebar is not set deep enough in concrete (something that is common around curved pool walls, benches, steps, and tight corners), it is more susceptible to damage.

Improper drainage is a known contributor (there should be a minimum of 3 inches between the earth and rebar), and tie wire has also been known to cause the rebar to rust. This is because after the soft wire disintegrates, a small hole where water can seep in is left in the plaster and shotcrete.

Finally, the cause of the stains may simply be that improper rebar work was done during the pool construction process.

How to Test Your Rusty Pool Stains

Before taking any action, it’s important to know what you’re dealing with. The easiest way to test the stain is to take some sandpaper and rub the area. If the stain disappears, then you know you don’t have a serious issue on your hands. If the stain continues to increase in size, severity or intensity, then it’s likely that the stain is coming from below the surface of your pool.

Another way to test for stains is to use other items you may already have at home. For suspected iron-causing stains, take a vitamin C tablet and hold it against the stain for approximately 30 seconds. If the stain lightens or disappears, it’s likely that iron is staining your pool. For decomposing organic debris, hold a trichlor tablet on the stain for 30 seconds. If the stain lightens, decaying organic material is likely the issue.

Pool supply stores also carry pool stain ID kits. These kits lead pool owners through a simple series of steps to determine what is causing the rusty stains in their pool.

Dealing with Different Rust Colored Pool Stains

Different approaches will need to be taken depending on what’s causing the stains in your pool.

For Organic Material

If the area is small, scrubbing the area and then vacuuming the pool should take care of the stains. Shocking the pool is also a great way to increase the free chlorine in your pool which will remove the rusty brown tannin stains.

For Metal Objects

Once the metal object has been identified and removed, brushing the spot with a steel brush or using a rust removing liquid will remove the stain.

For Metal in the Water

Some people opt to use magnets to gather the tiny bits of metal. But the easiest way to treat this issue is to use a metal removal additive that will filter out any excess metals. Sweeping and vacuuming your pool more often will also help reduce the effects of metal in your pool water.

For Rebar Stains

If you suspect your rust-colored pool stains are due to your pool’s rebar, the time to take action is now. Being extremely corrosive, the structural integrity of your pool has already been put at risk the moment you notice these stains.

The rebar may be fixed with there being water in the pool or with the pool being drained. Typically the more significant the problem, the more likely the pool remodeler will choose to do the job dry.

Your pool remodeler will start by chipping out the affected plaster with a chisel and hammer. Then, using a jackhammer, they will dig deeper into the gunite so the oxidized rebar is exposed.

Reputable pool remodeling companies will then follow the rust by chipping along the vertical and horizontal length of the rebar to determine how far the damage has gone. Once they reach clean steel on all ends, the affected rebar, as well as a few inches of unspoiled steel, is cut out using tools like die grinders, cutoff wheels, bolt cutters, and hacksaw blades. This is done to ensure that no rust is left behind.

Depending on the discussion a pool owner has with his or her pool remodeler, the pool rebar may or may not be replaced before it is patched. The patch then bonds with the concrete. The patch color may not always match the pool, in which case a pool owner may want to consider refinishing the pool.

Contact Your Local Pool Remodeling Company

Stains are unsightly and can pose a problem. Find a trusted, local pool remodeling company that can assist you with your issue to extend the longevity of your pool and keep it looking beautiful.