This is weird! I've replaced several heads and it has never used more than a trivial amount of ink.
Could this have something to do with old firmware? I have always done the head changes strictly at the printer, through the printer firmware. But I know it can also be done through the computer, I wonder if that leads to a different and more wasteful procedure?
I don't have the printer where I am now, but it is possible to create an overall status report file that tells you how many days the printer and the heads have been in use. The report also contains recent error codes, some of which pertain to print heads which have almost used up their full alternate nozzle allotment. For instance, on one tech support calls the tech commented based on error codes that the "other" head was getting near the end of its useful lifetime.
But basically, if the printer starts doing head checks and/or cleaning cycles at the end of more than very widely spaced printing cycles, you need to be thinking about head conditions.
You can find a lot of use 8300 maintenance information on the Canon Wiki page...
http://canonipf.wikispaces.com/BUT BE CAREFUL, sometimes it's not clear whether the wiki info refers to the 8300 or, for instance, the old iPF5000 which apparently does have a rather wasteful head change procedure.