Stain Identification

[TreeFiter]

So I've been working with two pools in particular that I thought had Iron staining. Both pools responded well to Citric Acid treatments, and both pools suffered from some degree of recurrence of the staining. The staining was rusty brown-orange in both pools. I recently sent out water samples from both pools to be analyzed for Iron, and in both pools the samples showed no Iron was present. I spoke with one of the chemists at the lab, and they said the staining was probably organic, and they see at least a few cases every year where organic stains are mistaken for metals.

So I'm not convinced. I still think I'm dealing with iron. How can I test the stains to verify or rule out the various causes? I've been told a trichlor tablet should remove organic stains.

Vitamin C will remove metal stains, but will it also remove organics?

Is it possible for organic stains to return once they are removed? I always thought they formed when organic debris sat on the pool bottom for a long period of time (like over the winter in a closed pool).

 

[chem geek]

Vitamin C (ascorbic acid) discolors iron stains rather quickly but won't fade organics very fast while Trichlor will fade organics more quickly and not fade iron so quickly. So usually you can distinguish iron from organics in this way. You are right that generally organic stains do not reappear. Such stains occur when something organic is physically touching the pool surface, usually plaster, and the higher pH from the plaster degrades the organic which then stains the plaster.