Jane - Where do you live and under what condition do you store your bulk ink? I'm in San Francisco and the ambient temperature in my house ranges from 55 to 70 degrees with an occasional spike (last heat wave) to about 85 during the day for less than a week. Higher temp storage would undoubtedly increase any changes brought about by a microorganism. Most ink vendors also suggest a two year shelf life for their inks. I originally bought my ink in 2 oz containers and then went to 4 oz. containers for the PC, PM, and Y inks as they are used in much greater quantities in the i960. I decided that the large dollar savings over OEM ink I experience, even with purchase of 2 oz containers, was sufficient and I didn't want to end up storing large quantities of ink with potential loss of quality as you describe. In addition, these printers have a finite life and I didn't want to end up with lots of ink on the shelf for a dead printer. This wasn't a problem for lots of years as the bci-6 carts were used by several generations of printers. Now, with the avialability of printers that use the bci-6 cart drying up, when my printerd die I will have to replace them with the newer chipped cart printers and purchase a different ink set.