Why your pool stains brown on well water — and why chlorine makes it worse

If your pool has developed a rust-brown, grey or purple-black tint on the plaster, the instinct is to shock it. On a well-fed pool around here, that instinct is usually wrong.

Organic or metal?

Two quick tells:

• Organic staining (leaves, algae shadow) is green-brown, often leaf-shaped, and lifts when you raise chlorine.
• Metal staining is rust-brown, grey or purple-black, spreads evenly, and gets worse with chlorine.

If a chlorine tablet held against the stain for a minute lightens it, it is organic. If nothing happens, you are looking at metal.

Where the metal comes from

Brunswick County’s public water is lime-softened specifically to remove excess calcium and iron from well-sourced supply, and plenty of properties here draw from private wells carrying iron and manganese directly.

Dissolved metal is invisible. It stays in solution until something changes — you shock the pool, or the pH climbs — and then it drops out onto the plaster.

What actually fixes it

A metal sequestrant, which binds the metal and keeps it in solution, plus corrected chemistry and patience. Not more chlorine. If you shock first, you set the stain, and removing it then becomes an acid job rather than a chemistry one.

If you top up from a well, a sequestrant belongs in your routine permanently, not just after a stain appears.