Too much pressure and you’re leaving the surface cleaner running in one spot too long. Check the orifice size on the surface cleaner nozzles. Make sure they are correct for the machine and that they give the desired pressure for the type of concrete to be cleaned. A year and half old concrete should not even need a surface cleaner. Water, Clorox, a stiff brush and rinse with a garden hose. You are doing permanent damage.
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