Brand new ink cartredge (2 weeks old, used daily) and the black, yellow and magenta work GREAT. But the cyan, its like it doesn't even exist. And it never did. It leave NO mark when I run the tests.
I have completed the cleaning cycle, then the test, then when that didn't work I did a deep cleaning cycle and that worked but its got some lines in it.

I am reluctant to clean it again, as it uses a lot of ink :(

Any ideas what the cause of this is?

The jets spit out ink in such tiny amounts that clogging is not surprising once in a while. Each dot on the page is one spit of ink.
Take it back to the store.

I already called, and they were more than happy to send me free replacements with their apologies :) thanks hon.