Fiberglass Pools: Why You Can Still Get Rust Spots

Pool owners may encounter a variety of oddly colored stains on the surface of their pool over time. Dark red and rusty brown stains are two of the most typical colors they’ll notice, which, while scary at first, may not always signal that something is significantly wrong with your pool. 

But why do they appear? Can they be avoided? How can you get rid of them? This is among the many questions that pool owners ask.  If this is your worry, then search no further as this article will answer all of your concerns. So continue reading!

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Why you can still get rust spots in your fiberglass pool

Fiberglass pools, like vinyl liners, have a sleek and smooth surface that repels certain stains, but they are typically not stain-proof!

The gelcoat coating protects the fiberglass shell, but surface scratches or crazing (tiny cracks) increase the likelihood of stains appearing as the pool ages.

There are various reasons why you could see stains in your pool. The following are some of the most typical causes of rust spots in swimming pools.

  • Organic material

Organic decomposing detritus on the pool’s surface, such as leaves, twigs, pine cones, and acorns, can cause rust-colored stains. These materials usually leave an imprint that reflects the stain-producing product’s form (such as the outline of a leaf).

  • Objects of Metal

Rust may be caused by everything from bobby pins to toy cars to nails in your pool. As soon as these things are detected, they should be removed. This is especially true if your pool water is quite acidic, as the more acidic your pool is, the more of a problem you’ll have.

  • Metal in the water.

If you see little rusty patches in your pool frequently, your water may include small metal pieces, known as oxidation of water. Iron in pool water is particularly problematic, and it may rapidly lead to costly repairs.

  • Rebar stains

The metal shafts beneath the plaster of your pool are known as rebar. If left untreated, the rebar will ultimately crack your pool’s shell. This will expose additional rebar, which will lead to more corrosion and the collapse of your swimming pool.

Rebar stains are frequently the result of inadequate covering around the reinforcements. Rebar is extremely susceptible to damage when it is not put deep enough in concrete (frequent around curving pool walls, benches, steps, and tight corners).

Improper drainage (a least of 3 inches between the soil and the rebar) is a known contributor, and tie wire has also been known to cause the rebar to rust. As soft wire disintegrates, a small hole in the plaster and shotcrete is left, allowing water to leak in.

So, the stains might result from poor rebar work during the pool construction procedure.

How do I get rid of rust spots in my fiberglass pool? 

Before eliminating the stain, it’s critical to identify the source of the rust to prevent having to remove the same stain repeatedly. Depending on the cause, the following different approaches can be employed.  

  • Regarding Organic Materials

Scrubbing the area and then vacuuming the pool should remove the stains if the area is small. Shocking the pool is also a good technique to boost the amount of free chlorine in the water, which will help to eliminate the rusty brown tannin stains.

  • For metal objects

The stain can be removed by scrubbing the area with a steel brush or using a rust removal liquid once the metal object has been discovered and removed.

  • For metal in the water

Some people prefer to collect the small metal fragments using magnets. However, the simplest solution is to employ a metal removal additive to filter out any extra metals.

Sweeping and vacuuming your pool more frequently will also assist in lessening the impacts of metal in the water.

  • Regarding Rebar Stains

If you believe your pool’s rebar causes your rust-colored pool stains, now is the time to act. Because these stains are particularly corrosive, the structural integrity of your pool is already compromised the minute you detect them.

When there is water in the pool or when the pool is drained, the rebar may be repaired. The more serious the problem, the more likely the pool remodeler will choose a dry approach.

Your pool remodeler will chip out the disturbing plaster with a chisel and hammer. They’ll then drill further into the gunite with a jackhammer to reveal the corroded rebar.

Following the rust, reputable pool renovation firms will chip along the vertical and horizontal length of the rebar to see how far the damage has progressed.

The afflicted rebar, as well as a few inches of unspoiled steel, is cut out using instruments such as die grinders, cutoff wheels, bolt cutters, and hacksaw blades once they reach clean steel on all ends. This is done to prevent any rust from forming.

Depending on the pool owner’s discussion with their pool remodeler, the pool rebar may or may not be changed before it is patched. After that, the patch adheres to the concrete.

The patch color may not always match the pool’s color, in which case the pool owner may consider resurfacing the pool.

How to Avoid Rust Spots in Your Fiberglass Pool  

It’s better to prevent stains in the first place than to clear up the mess later in a pool (or in life, for that matter). The following guidelines apply to all types of stains, regardless of their origin.

  • Keep the chemistry of your water in check:  This is very crucial in pool maintenance. This is because keeping your pool’s water levels in the right range will help you avoid an ideal range of issues.
  • Clean your pool regularly: Dirt, leaves, and bug corpses should be scooped or vacuumed away. This prevents stains on the waterline. By doing so, your water will appear to be more appealing.
  • Remove any metal artifacts that aren’t native to the area as well.

Learn How to Manage Your Pool and Hot Tub

Frustrated trying to keep your pool clear? Feeling confused about when to add the right chemicals? Get the perfect easy-to-use, illustrated ebook and video course today!


Yes! Rust spots may appear in your fiberglass pool. But you can now proceed with the confidence that rust stains will never scare/defeat you again! And as always, we wish you every success in your pool-maintenance endeavors. 

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