You're right. But what concerns me is that the copper coils would be happier with a PH sightly lower than 8 - 10.Nice setup, and it's always good to hear about a high level of dealer support.
Since put in operation, have you sampled your tank water? Is it clear or rusty? A big culprit for corrosion in a steel tank is low pH water. Test your water pH, you may be fine or you may have acidic water. IMO pH should be in the range of 8-10. Next big culprit is oxygen. Both can be easily and inexpensively dealt with to a reasonable level.