How do I adjust the suction of a hydrafacial machine so it doesn't damage the skin?

For hydrafacial cleaning, stronger suction doesn't mean better results. I've seen newcomers crank up the suction right away; the nose area might look clean, but the cheeks and forehead end up red, and the client complains of tighter skin the next day. Many skin issues aren't due to dirt, but a thin barrier; strong suction only makes redness more obvious. Before starting, I identify oily zones…