By Chris Marcano
Staining and water discolouration issues have plagued the appearance of swimming pools and hot tubs since the inception of the aquatics industry. These unsightly blemishes occur on pool and hot tub surfaces and can be a distraction from their desired appearance. They can be extremely frustrating, as well as difficult and expensive to remedy. Removing stains can be a complicated process which is often done incorrectly, resulting in wasted time and money, adding to the pool and/or hot tub owner’s frustration.
One of the main reasons why stains are so challenging to prevent and/or remove is because there is a great deal of confusion with regards to what actually causes them. For instance, metals, non-living organics, and even improper or poor techniques used in the construction of the pool all play a factor. In fact, these are all very different and all too common scenarios, which lead to the discolouration of underwater pool and/or hot tub surfaces. While this article will touch on many of these scenarios, the focus will be on the two most common causes of surface staining: metals and non-living organic stains. Further, exploring the specific remedies for these types of stains will shed some light on the issues, and hopefully eliminate the mystery and complications behind stain removal and prevention.
What exactly is a stain?
A stain is a discolouration that can be clearly distinguished from the surface, material, or medium it is found upon. Stains are caused by the chemical or physical interaction of two dissimilar materials (e.g. acrylic steps and the tannins from leaves, or a metal substance such as copper [Cu]). Unfortunately, in a pool or hot tub, stains can be caused by a number of different things. Believe it or not, some forensics may likely be required to determine the type of stain and the best course of action to remove it.
Stain identification
Pool and hot tub surface stains can manifest themselves in different ways. For example, a swimming pool stain could be a mysterious dark blob that appears overnight, or it could show itself as an ominously slow shadow that plagues the pool like an unwelcome ghost. They can also appear in many different incarnations, varying in size, shape, location, colour, and severity.
This litany of different manifestations and formations are two reasons why prevention and/or removal can be extremely confusing for the homeowner and professional alike. Using the stain categories shown in Figure 1 can help service professionals to better identify and treat stains that have developed on a pool or hot tub surface.
Green and brown
Green and brown stains, which appear on surfaces, are often caused by the tannins released from decaying plant debris and vegetation. Stains of this nature are classified as non-living organic stains.
Red and blue
These stains are also non-living organic in origin and more than likely caused by brightly coloured berries; check the area around the pool and/or hot tub for a source of such vegetation.
Blue, green and black
When a stain is a mixture of dark blue, green, and black, and there is no evidence of non-living organic matter, the stain is likely to have been caused by one of the following: copper that has leeched out of the heater due to poor water chemistry, trace metals found in source water, and/or inappropriately applied products like copper algaecide.
Green, brown and red
This combination indicates iron (Fe) as the source of the stain. Iron oxidizes very easily—even with low levels of halogens in the water—and can even appear after the iron contaminated water is exposed to carbon dioxide (CO2).
Black and purple
This dark colour combination is caused by manganese (Mn), another form of metal. Black discolouration can also be caused in plaster pools by black algae and should not be confused with a dark purple stain.
