Identifying stains: iron, copper, fungus, dirt, or something else?

Stains, spots, scale and more can be difficult for pool owners to identify -- and it's hard to fix problems, when you don't know what they are! The purpose of this post is to help you ID the problem; information about fixing it (once you know what you're dealing with) is elsewhere.

1. Note whether the stain is 'move-able' or not.

• Metal stains won't move or brush away.
• Black or gray fungal stains in vinyl LINERS will not brush away.
• Mustard algae will brush away.
• Dirt leaking through your filter or pollen will also brush away.

2a. If it's NOT 'move-able', test it or scrape it!

• Place vitamin C tabs on the spots -- iron will be lightened or removed.
• Place "Iron-Out" on the spot; both iron and copper stains will usually be removed or lightend.
• Place calcium hypochlorite (often: shock) on the spot: black algae or fungal stains will be lightened. Brush the cal hypo away, before it can bleach your liner!
• You can scrape a bit of black algae with your fingernail: it smears dark green on a 3x5 card.
• Black or gray fungal stains will SLOWLY be lightened by very high chlorine levels, but has no 'texture' and cannot be scraped or brushed off. (The stains are IN the liner material!)
• 'Sand' algae scale can't be brushed away, but bits will often flake or scrape off.

2b. If it IS 'move-able', see if chlorine affects it!

• Place calcium hypochlorite (often: shock) on the spot: mustard algae will disappear in a circle around the cal hypo. See below for an alternative method with liner pools.
• Feel it!
  • You won't feel mustard algae;
  • Pollen and dirt will be VERY fine particles with almost no texture;
  • DE powder will be fine particles but with a definite texture.
  • Leaking filter sand will feel like, well, sand.
  • Emerging green algae will feel slimy on vinyl and FG pools

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List of possibilities:

• Black algae
• Black copper stains
• Black fungal stains (from fungus UNDER the liner)
• Brown or tan pollen dust
• Brown-ish orange iron stains
• Brown or tan (dirty) DE powder from filter.
• Brown or tan filter dirt from malfunctioning filter
• Brown to greenish brown scale from 'sand algae' (white after bleaching!)
• Brown to black pine sap spots (initially clear, but they collect dirt and get black)
• Blue, green, bluish green copper stains.
• Yellowish, greenish, or tan mustard algae.
• Green algae

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