What's That Yellow-Brown Stain on My Swimming Pool's Walls?

stained swimming pool
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Many municipal and even some well water sources have iron as a contaminant. It can cause rust marks in the bathtub or toilet, and it can stain your pool.

First, what type of pool do you have? There are two types of pool surfaces that are susceptible to rust and staining: plaster pools and vinyl pools.

Types of Pool Surfaces Susceptible to Staining

Plaster pools are common among older swimming pools. With a plaster pool, you can expect to get a good five to seven years out of the plaster before  you need to refinish it.

Plaster was, and still is,  the most common type of finish. Essentially, a plaster pool is what many refer to as a concrete pool. The finish is a mixture of cement and water. Plaster finishes are more likely to stain because the surface of the finish is porous. While the finish appears smooth, it is not. This means two things: grime can seep in and become difficult to remove, and overtime, the plaster begins to chip away and erode. This allows rust to take up shop and hand out for awhile.

Vinyl is another pool finish that causes trouble. Vinyl is more resilient when it comes to staining, but it's not immune. Pool steps can leave stains and rust on the finish, and age can take a toll on the finish. The most common blemish, however, is usually fading caused by sun damage and tears caused by equipment or debris in the pool.

What Causes Rust in Swimming Pools?

There are a number of things that can cause rust spots and staining in a pool.

The steps are a common culprit, but any other metal items can blemish the surface as well. If you don't clean your pool frequently, or a hair pin manages to hide itself away, rust can flourish because the items sit in one place and begin to rust. In addition to steps, rust can be caused by hair accessories that have been forgotten, old pipes, metal drains and light fixtures in the pool, nails, and other metal debris.

Vinyl pools with steel fasteners and copings are especially troublesome.

Checking for Rust

A really easy test to confirm an iron stain is by using vitamin C (ascorbic acid). Get a generic Vitamin C tablet and rub it on the stain, and it should come off easily.

Getting Rid of Rust

There are many effective products available to remove iron stains. You can get swimming pool stain removal products at your local pool store or you can find swimming pool stain removal products on PriceGrabber.

Additional techniques include:

  • rubbing large vitamin C tablets on the stain
  • placing a pip over the stain, with the other end sticking up out of the water, and pouring a dry acid down the pipe to it sits on the stain. This requires protective equipment such as gloves, goggles and protective clothing. Hold the pip in-place for at least one minute before slowly removing it.
  • hiring a professional pool cleaner or visiting the pool shop for advice 
  • refinishing your plaster pool or replacing the old vinyl

Here's a tip: if it doesn't come off with a vitamin C tab or stain remover, call the pros. Don't risk damaging your pool. If you have many rust spots or large smatterings of rust on the pool's surface, you have a bigger problem that must be addressed by pool pros.