Why Has the Stone Around Your Pool Deck Turned Green and Black? If you have natural stone installed around your pool and it is not properly cleaned and maintained, it can begin to grow a green and black substance that is less than lovely to look at. Keep reading to learn what this is, why it happens, and how to clean it. Or contact Fuller Stone Care at 855-205-0972 and let us clean and prevent it for you.

It is Likely a Biological Growth

In almost all cases, any green and black spots on natural stone pool decks occur as a result of biological growth such as algae, mold, lichen, or moss. In some cases, ivy or grass could cause this look too. Keep reading to learn more about each of these potential growths.

Algae is Not Always Green

Most people assume that if there is any color other than green, then it must be something other than algae. This is not necessarily true. Algae is most often green, but it can also be yellow, red, orange, or black. It is easy to determine that it is algae if it is growing in a mat, film, or patch on the surface of the stone. That is because it is a single-cell organism that does not have leaves, roots, or stems.

Moss Is Not Always Green

Likewise, while moss is most commonly green, it can also be red. It is similar to algae in that it requires sunlight and moisture, but it also needs a mineral source – which is most often sourced from the soil. Moss is also unique from algae in that it has a root structure along with very small leaf structures. It can grow in the grout.

Mold is Not a Plant

It is also possible that the substance is mold. Many people don’t realize that mold isn’t even a plant at all – it is a fungus. It does not require any sunlight, but it does require moisture and a food source. It is generally black, but it can be black, yellow, orange, brown, or red too. While any natural stone can sustain mold growth, it is most common in limestone because of the organic matter that can feed it.

Lichens Live with Other Substances

Lichens are another type of fungus, and they live only with algae or cyanobacterium (a relative of bacteria). This substance can be red, green, yellow, or white. You can identify these by their crusts or leaf-like structures that have defined borders that grow away from the surface of the masonry or stone.

We Can Clean Your Stone

If your stone looks less than perfect, then we welcome you to contact Fuller Stone Care at 855-205-0972 to learn about cleaning and maintenance options. We are standing by to answer any questions you have, to help you find the right method to remove the substances, and to get back to the beauty of the natural stone.