Pool Stains and How to Remove Them

Stains and discoloration on a pool’s surface can occur in a lot of colors and can be caused by a variety of reasons. Identifying the type of stain and determining its cause is crucial to remove it.

how to remove pool stains

Types of Pool Stains

Based on the color of the stain, it can be easy to determine its cause. Pool stains can be broadly classified into the following color groups:

  • Reddish-Blue: These bright stains are very easy to identify and deal with. These are usually caused by squished berries that have made their way into the pool. Look out for any berry-bearing shrubs or bushes around the pool and act on them. Trim away any branches that might cause the berries to drop into the pool.
  • Greenish-Brown: These dull-looking stains could be caused by organic matter like algae, dirt, leaves, etc.
  • Greenish-Blueish-Black: While a lot of greenish or blue stains are caused by organic matter like algae or leaves, this could also be due to corrosion from copper plumbing.
  • Greenish-Brown: Most brown tinges hint at metal residue. This could be due to rust from pool equipment or from other items near the pool that are made of iron.
  • Brownish-Purple: This can be a very dark stain, almost leaning towards black. This could be due to manganese present in the source water.

Determining the Cause of Pool Stains

Pool stains can be caused due to organic matter or metal residue that is contaminating the pool. To check for organic stains, apply a dab of chlorine onto the stain.

Chlorine kills organic matter and thus should easily remove smaller organic stains. If the stain does not get removed, it could be due to metal residue.

Green or black stains can also be stains due to black algae. To test whether these are due to metal or algae, conduct the vitamin C test by holding a vitamin C tablet against the stain for 30 seconds.

If the stain does not change, it is algae. If the stain lightens or vanishes, it is due to metal.

How to Remove Pool Stains Caused by Organic Matter

To eradicate organic matter from pools as well as remove the stains caused by them, a chlorine shock can be the best method. To do a chlorine shock, here are the steps to follow:

Test the Alkalinity and pH Levels

Use generic pool water testing kits to assess the balance of the water. Add any necessary chemicals or dilute the water if necessary. Ideally, the alkalinity should be 100 to 150 ppm and the pH should be 7.4 to 7.6.

Shock the Pool

Shocking a pool involves adding high amounts of chlorine to the pool to kill bacteria and organic contaminants. Sprinkling granular chlorine shock over the stained area should make the stain disappear almost immediately.

If there are multiple stained areas or a large number of organic stained regions in the pool, this may not be enough. In such cases, tripling the dose of chlorine can do the trick.

Scrub the Pool

If there are traces of the stain still remaining, a good scrub or brushing should take care of it. Use a scrub brush or a stain eraser and gently rub across the stain. Keep the pool pumping for the next 8 hours or overnight and repeat the scrubbing for the best result.

How to Remove Pool Stains Caused by Metal

Metal stains can occur in various parts of your pool like the walls, surfaces, around pool equipment and even in the water. Once you’ve determined that the cause of a particular stain is due to metal, here’s how to act on them:

Lower the Chlorine Level

Use a neutralizing chemical to completely remove any chlorine from the water and bring the chlorine level to 0.0 ppm. This is necessary as chlorine can cause more stains during this stain removal process.

Lower the pH Level

If the pool water is at a higher pH, it could lead to more metal stains. You can use muriatic acid to lower the pH.

Turn the Pump and Filter On

For stain removal, you will need continuously circulating water. So, turn on the pool pump as well as the filter before proceeding with the stain removal.

Add Ascorbic Acid

Add 1 pound of ascorbic acid for every 10,000 gallons of water in the pool. Let this circulate through the pool plumbings as well to remove any other spots that might be currently invisible.

Check this every 30 minutes and add more ascorbic acid directly on any stains that are still visible. The metal stains should ideally go away within 24 hours.

Prevention of Pool Stains

Once you get rid of these stains, it’s now time to ensure that more such stains do not return. Here are a few tips to keep pool stains at bay:

  • Keep an eye out for stains and act on them while they are still small.
  • Keep the pool water clean by removing leaves, twigs and other such matter that might have made their way into the pool.
  • Maintain a healthy chemical balance and pH level in the pool water.
  • Do regular vacuuming and cleaning of the pool’s surfaces.
  • Keep organic matter like plants and trees away from the pool.
  • Test your source water to see if this is bringing any stain activators into the pool. Use the necessary filters to filter out such matter from the source before filling the pool.
  • Use a metal binder or sequestrant. These kinds of chemicals bind with any metal particle in the water such that they do not get deposited on the pool’s surface.
  • Check your pool plumbing regularly for corrosion.

Final Thoughts

This was a deep dive into different types of pool stains, their causes and ways to get rid of them. By knowing the exact cause of these stains, removal becomes much easier.

Once you’ve removed existing stains, preventing more stains becomes very easy. It’s time to enjoy your pool without worrying about these worrisome stains. Enjoy your swim!

michael keenan author

Author - Michael Keenan

I'm Michael Keenan the owner and creator of the Outdoor Care Guide. I'm a trained horticulturist with over 30 years experience in pool care, plant care and landscape care! Seemed like a good idea to share - I think I can make your life easier and save you some time and money!