Opened our pool this year for the 6th time and came across this stain in the deep end. Scrubbed it - didn’t budge. It almost looks like a super clean spot in the middle surrounded by yellow. We tried chlorine in a sock and vitamin c in a sock and it has not improved. Water chemistry is PERFECT. the algecide we used to close isn’t the metal based stuff as it turns my hair green. What could it be!?
pH = 7.2
TC = 3.5
FC = 3.0
Alkalinity = 130
Hardness = 0
Buffalo,NY
Chlorine pool
Vinyl liner
20x40
Forgot what else would be helpful…
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