There are many different type stains that appear on
pool surfaces. The color is a clue both to what it is
and what is causing it.
Some people mistakenly think that algae is a stain
when mostly algae is removable through proper
maintenance and balancing of the chemicals.
For more information on algae see Chemicals.
What causes the different colored stains on my plaster?
Minerals and other substances find their way into every pool. Iron, calcium and copper exist
naturally in source water, and can be prevalent in well water.
While other materials can stain plaster and vinyl just as easily - sources include organic matter
such as leaves, and excessive oxidizer - dissolved minerals remain one of the most common
In an ideal world, pools would never suffer from stains because their perfect water balance
would hold metals in solution all the time. In reality, though, pH and alkalinity can drift and
calcium levels can climb, leading minerals to fall out of solution, or precipitate, and
The key is maintaining a good chemical balance to avoid the ups and downs, but sometimes
change is impossible to avoid. To combat this problem, we try to keep chemicals balanced at
all times but in between our service calls, change can occur. In this case we use sequestering
agents, which hold metal ions in solution so they do not precipitate and form stains and
deposits on walls and floors. We also use chelating agents which use an electrical bond
between the agent and the metal ions. This holds it in a form that can now be more readily
filtered out. This is part of your service with us.
The following is a list of minerals and the color of their stain:
Calcium - usually white crystals adhering to the pool plaster.
Cobalt - fiberglass shells - red, blue, gray and black.
Copper - Blue, green, black, teal and dark red.
Iron - Dark red, brown, black, gray and green.
Manganese - Pink, red and black.
Many of these stains can be removed with acid washing the pool plaster. Success really
depends on how deep the stain goes into the plaster, as acid washing removes a small
amount of plaster. See acid washing.
I have lots of little rust stains around the return lines of my pool. What causes this?
This is usually an indication of a deteriorating heater. Time and chemicals and wear and tear
can break down a heater quite easily. The water is always traveling through the heater and the
heat exchanger where corrosion can easily occur.
Larger rust stains can be rebar showing through the plaster. These are the steel strengthening
rods under the plaster, in the concrete and gunite. This just means that your plaster is very thin
and you may be in need of a replaster.
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