How to identify and remove pool stains

Look at the color, look at where it is, then test it. Two tests cover almost everything:

• Vitamin C test. Hold a crushed vitamin C tablet against the stain for 30 seconds. If it lightens, it is metal: iron, copper or manganese.
• Chlorine test. If vitamin C does nothing, brush the spot and dose a little chlorine near it. If it fades, it is organic or algae.

A stain that ignores both is often in the plaster itself, which is where an acid wash comes in.

Leaves or iron. Leaf stains are brown or tea colored, often in the outline of the leaf, and sit where debris settled on the floor. They fade with chlorine and brushing. Iron stains are rust brown or orange, often spread across a wall or near where the fill water comes in, and they react to vitamin C, not chlorine.

Iron is very common on well water here. See how to remove well water stains.

Usually mustard algae, especially if it is a yellow film on the shady side of the pool that brushes off like dust and comes back in the same spot. In spring, yellow pollen floating on the surface and collecting at the waterline gets mistaken for it. Yellow brown can also be iron.

How to tell pollen from algae, and how to get rid of it, is in how to get rid of mustard algae.

Raised black or blue black spots that feel rough and come back after brushing are almost always black algae, and they love grout lines and rough plaster. Flat dark stains that react to vitamin C are metal, often manganese, which some well water carries. Dark lines in plaster cracks are often just dirt packed into the crack.

Black algae has its own guide: how to get rid of black algae.

Copper. Blue green, teal and turquoise patches that ignore chlorine but lighten with vitamin C are copper, usually from a corroding heater, copper algaecide or an ionizer. Purple or violet stains usually point to copper too, in pools carrying a lot of stabilizer. See how to remove copper stains.

Mostly things that sat there. Leaves and acorns leave brown outlines. A bobby pin, nail or coin leaves a small rust spot. Granular shock or calcium poured straight onto the floor instead of dissolved first can bleach or mark the plaster. Metal that comes out of solution also tends to settle near the main drain.

Keeping the floor vacuumed and the debris out is half the battle, and it is a big part of every weekly pool service visit.

With ascorbic acid while the pool stays full, then a metal sequestrant to hold the metal in the water so it does not settle back onto the plaster. Iron and copper both respond to it. Copper has its own step by step in how to remove copper stains, and iron from a well is in how to remove iron and well water stains. Metal that has set deep into old plaster needs an acid wash instead.

Most of them, yes. Organic stains fade with chlorine and brushing. Metal stains lift with ascorbic acid while the pool is full. Draining is for stains set deep in the plaster or plaster that is worn out, and acid wash or resurface explains how to tell which one you have.

Whatever you treat with, keep pH and chlorine in the CDC ranges afterward so the stain has nothing to come back on.