I am currently in my 3rd heating season and have had no problems. I believe they now make the exchangers out of materials that resist corrosion and mineral buildup. It may also depend on water quality. I haven't had my tested for hardness, but there are not obvious deposits like iron stains etc. I have a 1000 sq ft greenhouse that gets white mineral deposits from watering, possibly calcium carbonates? The water in my pond is currently 9 ft deep and crystal clear. I can see at least 6 ft down.
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