A few months ago, I posted to this forum several times about problems I was having with non-oem inks in my IP5000. I had tried both Procolor cartridges (which use Formulabs ink) and Hobbicolor bulk refill ink, and in both cases I found that there were gross color differences between the photos I printed with these inks and older prints of the same photos which I had made with OEM ink. In all cases, the problems seemed to involve magenta, at varying times there seemed to be either too little or too much. I did multiple nozzle checks, but the tests always seemed to indicate that the nozzles were firing properly.
A few weeks ago, I noticed some odditiies when I ran a nozzle check. The light magenta strip was very faint and irregular. Even stranger, the darker magenta strip alternated darker and lighter bands. Each band was about one inch long, and there was a hard edge between the darker and lighter portions. This pattern repeated itself on subsequent tests, and its precise regularity implied that the problem wasn't clogged nozzles, but some sort of electronic or software issue. Repeated cleanings and deep cleanings made no difference.
I finally called Canon tech support and described the problem. They had me remove + replace the printhead, run deep cleaning again, etc. When none of this helped, the tech told me that I had either a defective print head or a defective purge unit (I think that's the name he used), probably the former. The tech told me that the problem with the alternate bands of lighter and darker color within the heavy magenta strip of the nozzle test was a known issue, and occassionally showed up even in new printheads. (Actually, I don't know whether this problem always occurrs in the dark Magenta strip, or if it also can occur in the other colors). Since my IP5000 was still under warranty, the tech agreed to send me a new printhead.
Installing the new printhead immeadiately fixed the problems I was having with the Nozzle check test, and more importantly it also eliminated nearly all of the differences I had been seeing between my new prints made with non-oem ink, and the older prints made with Canon ink. So please ignore my previous posts complaining about color inaccuracies with Formulabs and Hobbicolors ink!