How do I know if my pool stain is metal or organic?

Press a chlorine tablet on the stain for 30 seconds. If it lightens, it is likely organic. If a vitamin C tablet lightens it instead, it is likely metal.

What causes brown stains in a pool?

Brown stains are usually organic, from leaves and debris, or iron, often from well water. The quick stain test helps tell them apart.

Why does my pool have blue-green stains?

Blue-green or teal stains usually point to copper, which can come from corroding heater parts when pH runs low, or from copper-based algaecides.

Will shocking my pool remove stains?

Shocking can help with organic stains, but it can make metal stains worse. Identify the stain type first.

How do I prevent pool stains?

Keep debris out, keep pH balanced, test fill water for metals, use a sequestrant if needed and test your water regularly.

Water Care October 31, 2026 5 min read

Pool Stains: Metal vs Organic and How to Remove Them

The color of a stain tells you a lot about what caused it, and how to get rid of it.

Written by Pool Supply Atlanta Team

Pool Stains: Metal vs Organic and How to Remove Them

Most pool stains are either organic or metal. Organic stains come from leaves, algae and debris and are usually green, brown or black. They often lighten with chlorine. Metal stains come from iron, copper or manganese in the water and are usually rust-colored, blue-green, purple or black. They often lighten with ascorbic acid (vitamin C). Identify the type first, then treat it, then fix the cause so it does not come back.

What the color usually means

Stain color	Likely cause
Green or brown	Organic debris like leaves, or algae
Reddish brown or orange	Iron, often from well water or rusting metal
Blue, green or teal	Copper, often from corroding heater parts or copper-based algaecide
Purple or black	Manganese or copper, or black algae if the spots are raised and rough
White or crusty	Calcium scale from high calcium or high pH

The quick stain test

Not sure if a stain is organic or metal? Try this:

Press a chlorine tablet against the stain for 30 seconds. If it lightens, it is probably organic.
Press a vitamin C tablet against the stain for 30 seconds. If it lightens, it is probably metal.

Wear gloves, and remove any tablet from the pool afterward.

How to remove organic stains

1Remove leaves and debris from the pool.
2Test and balance your pH.
3Shock the pool and brush the stained areas well.
4Repeat brushing over the next few days as the stain fades.

Organic stains often clear up with good sanitizer levels and regular brushing. Stubborn spots can be treated directly with chlorine applied to the stain.

How to remove metal stains

Metal stains need a different approach, because shocking can actually make them worse.

1Test your water, including metals if possible.
2Treat the stain with an ascorbic acid based stain remover, following the product directions. This usually involves lowering chlorine and adjusting pH first.
3Brush the stained areas to help the treatment work.
4Add a metal sequestrant to keep dissolved metals locked up so they do not restain the surface.
5Rebalance your water once the stain is gone.

Not sure what is staining your pool? Bring a water sample and a photo of the stain to our Alpharetta store at 2900 Holcomb Bridge Rd. We will help you figure out the cause and the right fix.

Call 678-691-6124 Get Directions

Calcium scale and black algae

White crusty buildup is usually calcium scale. It forms when calcium hardness or pH runs high. Light scale can be treated with a scale remover and better water balance, but heavy buildup may need professional cleaning. Read our guide to cloudy pool water, which covers high calcium too.

Black algae shows up as raised, dark spots with roots that dig into plaster. It needs aggressive brushing and treatment. See our guide to clearing a green pool for the algae treatment steps.

Safety first

Never mix pool chemicals together. Always follow product label directions, add chemicals to water rather than water to chemicals, and wear gloves and eye protection when handling them.

How to stop stains coming back

Keep leaves out of the pool, especially in fall. See our fall leaves guide.
Keep pH in range. Low pH can corrode heater parts and release copper into the water.
If you fill your pool from a well, have the fill water tested for metals and use a sequestrant.
Test your water regularly so problems are caught early.

When stains mean something more

If stains will not come out, keep returning quickly or the surface underneath is rough or etched, the finish itself may be worn. Read our guide to acid wash vs resurfacing to see what your options are.

Frequently asked questions

Get to the bottom of your stain

Bring a water sample and a photo to Pool Supply Atlanta, 2900 Holcomb Bridge Rd, Alpharetta, GA 30022 for a free computerized water test. Open Monday to Friday 9am to 5pm and Saturday 9am to 4pm. Serving Alpharetta, Roswell, Milton, Johns Creek and Sandy Springs. Questions? Call 678-691-6124.