For your info the black ink is the only one with different versions for photo (glossy) versus matt papers, ie photo black and matt black. All the other colours are used for both photo and matt papers. This is also true for Epson and HP printers apart from some Canon and HP models that also have a gloss optimiser 'ink', which is effectively a varnish.
Thanks. Talk to support and it looks like it does not matter what media I use. If I leave it on, every 24 hours it will clean all the nozzle shooting off all colors, so even if I do not use any photo black for long time, it will take care of itself.
BTW, if you hold down the Load+Navigate and then Power button (and hold the Load and Navigate for a bit longer), then it will put the printer in the special mode where it can test print. It looks like the Photo Gray on the right printhead is causing an issue. It came out very slightly fainter on a small part of it. So, it seems to be printhead problem and not something else.