I love the CCTV fluid ink animation and would like to create one, does anyone have any idea what they used to create it and how it was done?
You have 3 options.
The first option is by far the easiest, the second requires some knowledge of lighting, a decent camera, some experimentation and is a lot of fun, the third is slow to render and expensive.
Once you have your patterns use procedural mattes or color effects and overlays to create the different colors. It's as easy as that. You cannot do realistic fluid ink animations inside that look like ones. You may be able to get close with Particular, but that's about your only option inside AE.
Directly from the Vimeo page for the CCTV video you can see that the ink was filmed for their project:
Ink&Footage: Thore Bornemann, Felix Martens