Welcome to TFP! The staining from the roofing project could be metals related. For those, I would first try rubbing a basic Vitamin C tablet on a stain to see if it disappears. Just rub the tablet right on the stain to see if it lifts. As for the pavers, can you post some pics? I only see the pebble images. If it was indeed muriatic acid, it may have permanently effected the pigment of the pavers.
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