Swimming Pool Stains & Discoloration

February 24, 2010 at 4:13 pm 3 comments

One of my favorite swimming pool product lines is produced by Jack’s Magic. They are industry experts on everything you would ever want to know about pool stains and pool water chemistry.

With their help, I’m creating a series of articles that will educate you on swimming pool stains, so that you can keep your pool looking beautiful all year long!

Most people assess the “well being” of their pool in three simple ways:

  1. Is the water sparkling clear?
  2. Is the pool free from algae?
  3. Is the pool free from stains?

In this month’s featured article, Familiarization with Stains and Discoloration, we will focus on number three — staying stain free!

Featured Article: Familiarization with Stains and Discoloration

The goal of these articles is to make you aware of and familiar with the major stains and discoloration most commonly found in swimming pools — and to provide you with an understanding of how properly balanced water plays a role in stain development. Pools do stain, even with balanced water.

When you finish reading this set of articles, you will be able to…

  • Identify the most common pool stains and discoloration.
  • Efficiently carry out the Stain ID process to determine the proper treatment.
  • Intelligently and accurately locate the factors that may have contributed to the discoloration.

A properly maintained pool is an ongoing source of satisfaction and enjoyment. As a pool owner, you depend on professional advice to keep your pool operating correctly and looking its best.

Stains and discoloration come from a variety of sources and are in many forms; most of which, you have no control over. Everything Jack’s Magic does, should be based on properly balanced water. Properly balanced water is your best friend, whereas, unbalanced water can be a catalyst for staining, scaling and discoloration.

There are two types of pools:

Those that are stained…and those that are going to stain!

Types of Discoloration

  • Organic Discoloration
  • Inorganic Discoloration / Stains

Common Organic Discoloration:

  • Discoloration: Scale
  • Characteristics: Hard, crusty build-up on pool interior
  • Possible Causes: High pH and/or alkalinity; excessively high calcium
  • Discoloration: Green Algae
  • Characteristics: Greenish tint to water and/or green deposits on pool surface
  • Possible Causes: Rain, heat, low/no sanitizer level

Green Algae

  • Discoloration: Mustard Algae
  • Characteristics: Brownish-yellow, wispy — will brush off easily, but reappear; often found in shaded areas
  • Possible Causes: Rain, heat, low/no sanitizer level, contaminated swim suits

Mustard Algae

  • Discoloration: Black Algae
  • Characteristics: Black spots or clusters; has “roots” which can penetrate finish
  • Possible Causes: Continually low sanitizer levels

Black Algae

  • Discoloration: Pink Slime (bacteria)
  • Characteristics: Pinkish-red; usually more prevalent in biguanide pools
  • Possible Causes: Rain, soil, contaminated swim suits; grows in circulation piping

Pink Slime

  • Discoloration: White Water Mold
  • Characteristics: Resembles small, floating pieces of white tissue paper
  • Possible Causes: Low/no sanitizer; grows in circulation piping

White Water Mold

Inorganic Discoloration/Stains:

In our next article, we will go over inorganic discolorations and stains.

Thank you for reading!

Do you have questions about pool stains? Email me any time at Owner@LightningPoolSupply.com or leave a comment below!


Chip Payson – Owner of LightningPoolSupply.com


Entry filed under: Stains and Discoloration. Tags: , , , , , , , , , , , , , , , , .

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3 Comments Add your own

  • 1. Chris  |  September 3, 2010 at 11:54 am

    Good to know!

  • 2. Chris  |  June 27, 2011 at 12:57 pm

    I teach water aerobics and for the first time in my life the pool i teach at discolors our bathing suits from purple to pink, blue to grey and eventually falls apart.

    I’m trying to determine the cause of this happening and if in fact the pool is safe for our skin.

    Any insight you have, would be greatly appreciated.

    • 3. lightningpoolsupply  |  June 29, 2011 at 1:46 pm

      It sounds like too much chlorine but I’d need a little bit more data to know for sure. Can you tell me what PPM the chlorine is kept at on average? Also, are you required to keep the chlorine PPM above a certain level, if so what is the minimum required?


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