Air is one of the biggest problems with Continuous Ink Supply Systems, when air gets into the systems it can produce poor print outs. The air is normally visible in the feed tubes from the ink reservoirs.
It is normal for small amount of air to enter these tubes without effecting your print outs and will purge by itself, if your printouts are effected and air in the tubes is the cause then the following videos may help you solve the problem.
Remove Air from Epson CISS Video 1
Remove Air from Epson CISS Video 2
Remove Air from Canon CISS Video