Need quick confirmation that I'm dealing with iron

[jenmenke]

Mustard algae can be chlorine resistant.

Do the Pool Chart; do the chlorine test I mentioned.
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I'm not sure I understand: you mean sprinkle granular chlorine on to the wispy, easily brushed away orange and then try really hard not to disturb it? Since I only use bleach, I don't have any granular chlorine. Can I crush up a puck? I think I have a few of those. Let me know