Dark Brown / Black Stains That Won't Scrub Off

[greatlakes]

Hi All,

I'm new to the forum, but have been lurking and reading for awhile. I have a 20,000 gal saltwater pool. All the chemistry parameters and values seem to be at acceptable levels and the water looks great, although the chlorine levels continually seem to be on the low side despite running the salt water generator at a high level and adding chlorine shock somewhat regularly.

These stains simply won't scrub off. I would love some feedback on how to address this issue!

Thanks!

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[zea3]

Hi, welcome to TFP! Please post a current set of test results. What are acceptable levels according to the pool industry are usually different than what we recommend at TFP, and the test results help us rule out some of the possible causes of your current problem.

Have you tried scratching any of the black spots to see if they scrape off? How old is the plaster? Is the plaster pitted?