My sister opened her pool this year and found a huge stain covering the deep end. They didn't check their pH at all last summer, the water was so acidic it ate the copper in the heat exchange, which settled over the winter.
They had a new heater installed - Sta-Rite SR333NA - and the pool store guy recommended Metal Magic to remove the stain.
I'm guessing we don't want Metal Magic going through the heat exchange. My heater has a manual bypass, the SR333NA does not. There's a brief mention in the Sta Rite manual of a bypass switch. So my question is, does water flow through the heat exchange when the heater is off? Or do I need to manually bypass the heater while we're using Metal Magic?