Canon Pixma iP90 User Manual page 49

Note To maintain optimal print quality, use an ink tank
within six months of its first use.
Once an ink tank has been used, do not remove it
from the printer and leave it out in the open. This will
cause the ink tank to dry out and the printer may not
function properly if it is reinstalled.
Color ink consumption may occur even when black-
and-white or grayscale printing is specified.
Color ink is consumed in the head cleaning and deep
cleaning, which are necessary to maintain the printer's
capabilities.
When an ink tank runs out of ink, replace the ink
tank with a new one immediately. If printing is
continued with no ink in the ink tank, a problem may
occur. And, the Low Ink Warning dialog which tells
the exchange time of an ink tank cannot be indicated
properly.