Low pH will, indeed, eat the copper from your heat exchanger in very rapid order. I see this a lot on apartment and hotel/motel pools where high use makes good water chemistry a very difficult thing to control. It is also very common on fiberglass and vinyl-liner pools wher the pH tends to be low if not cared for regularly.

High water velocity (pump too large) will also do a similar thing to the exchanger.

These are both beyond the control of the manufacturer and would happen to any brand of heater.