Do not go after it with high pressure! Using your downstreamer, put 2 gallons muratic in a five gallon bucket, then inject that at about a 1:12 ratio with your downstream injector working on small areas at a time. Then soft rinsing very thoroughly quickly after applying the acid. Works great on construction stains like red dirt. Do not use a surface cleaner for at least a year or you may find yourself taking off the creme.