The ink level did not go down at all for my photo black because the rubber washer did not have a good seal.
Since your cyan ink level go down but not as fast as the other color, I think you have flow problem due to the cartridge as dougsewell pointed out. Test it with a new Canon OEM cyan cartridge.
At the mean time, if you can dilute the cyan ink by putting a few drops of Windex on the exit port of your current cyan cartridge. You should get a near perfect nozzle check after a clean cycle.
Since your cyan ink level go down but not as fast as the other color, I think you have flow problem due to the cartridge as dougsewell pointed out. Test it with a new Canon OEM cyan cartridge.
At the mean time, if you can dilute the cyan ink by putting a few drops of Windex on the exit port of your current cyan cartridge. You should get a near perfect nozzle check after a clean cycle.