Try sending a private message yo Pedlars Pen in the main firum here, also check his thread about pens on the main P& I page, he may have some ideas.

I second all of the above posts’ cautions about using Indian or acrylic inks though a fountain pen , further I would suggest you might like to try “Winsor & Newton calligraphy Ink” – you can only use the ink sold with blue coloured tops though a fountain pen in this range (NOT red coloured tops.) , & even then you shouldn’t leave it lying unused for very long because it might become blocked.
This ink is permanent & will not fade on exposure to light, so you can hang your work on the wall & it will last a long time.
It is thick & of a rich saturated colour.
I would recommend this ink above all others that I know for your PPP, as long as you Scribble a line or two on a scrap piece of paper every few days you will be fine.
You will find this ink will give you the richest / darkest & most saturated colour of all the inks.

Another ink coming in a close second would be “Higgins Eternal” (Black only), this “eternal” name refers again to it’s permanency, it is not quite as rich & intense as the W&N I mentioned first but when used through a PPP it is fine because of it’s very “wet” flow. Again this is an ink to keep using or scribbling on a piece of scrap to avoid clogging the pen.

I would advise against using any normal fountain pen ink because they are dye based & will fade on exposure to light.
However if you are journaling etc. where the work will be in a book- hidden & protected from the light that may not be a consideration.
In that case the fountain pen ink “Pelican 4001” series (black colour only) would be fine too, although the only advantage over the other inks I mentioned would be that you could leave it unused & forgotten about for ages & no harm would come to it.
Have fun ! Mike