We're in the process of restoring the decking and coping of our early 80's pool. The coping structurally is in good condition, however, there are deep black stains in most of the stones. Initially, we tried watered-down versions of 10% chlorine bleach and 20% muriatic acid, brushing each in and letting it sit for quite some time, then lightly pressure washing. That didn't do anything so we moved on to testing both just straight which also didn't do anything at all. All the chemicals were brand new and I'm out of ideas of anything I would have stronger at my disposal. is it possible that the stains are just too far embedded in these old stones?
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