What usually causes stains on the interior pool surfaces?

Stains on the interior surfaces of a pool can be attributed to various metals, which often originate from water sources, equipment, or even pool chemicals. Copper, manganese, and iron are commonly known culprits, as each can interact with pool water in different ways and lead to staining.

Copper stains often appear as blue or green marks and can occur when copper-based algaecides are overused or when the pool water has a high copper concentration due to plumbing fixtures or heating systems that introduce copper into the water.

Manganese can cause dark brown to black stains, typically the result of high levels of manganese in the source water or from pool maintenance products containing manganese. Its staining effect often requires more significant treatment to remove.

Iron tends to manifest as reddish or rusty stains and is frequently introduced through source water or corroded metal fixtures. It can be particularly problematic in areas with high iron content in well water.

Since all three metals can cause staining, it is accurate to say that each contributes to the phenomenon in specific ways, making the comprehensive option, which includes all of them, the correct answer.