I have owned a Pinguicula "Encantada" [laueana "CP2" x moctezumae] for quite a while and it has never done very well. I have always had it in a inorganic soil mix, with a small amount of John Innes or peat added. I've tried several mixes but they are all primarily inorganic. The reason for me using these is because I have read in several places that people use a mix of perlte, vermiculite, sand etc etc. A few weeks ago I decided to try something completely different - as the plant wasn't doing well so I'd got little to lose - I repotted it in Levingtons multi-purpose compost with a little added perlite. This is a peat based compost with added recycled organic matter and nutrients. To my surprise the ping has taken on a growth spurt, in fact it has grown more in the last few weeks than it has in months. I read in a post recently that Stephen (gardenofeden) also has his Mexican pings in a mulitpurpose compost - a peat free one.

This is not to say that inorganic mixes are not good in all cases - I have a gypsicola x moctezumae growing in a mix or seramis, vermiculite, perlite, sand and tufa and it grows well.

There's just way too many mixes / combinations / variations out there and not enough true scientific testing. Except for a few people have tried a bazillion different things, over the decades, most of us are going but what we read or what we happen to fall into - me being one. Joseph Clemens recommended to me crushed coral. So I use it. Personally, I put a small layer of LFS at the bottom, partially to keep the rest of the media from falling through and retention of a little moisture. Then I mix sand and eggshells and crushed coral. I do also have perlite but perlite turns green. I can do without perlite! But it's more than just media. Good lighting and feeding have also led to plants that are 4-5" in diameter and pink / purple colouration.