@Tom
I just had the first hatch in the clutch I incubated in vermiculite/peat mix. This is a younger female I mentioned before that has have very low fertility rates. I put these eggs without any rinsing into a container of 50/50 vermiculite / peat mixed completely and then an equal weight of water added and mixed. This produced a slightly wetter mix than I normally had used as the peat was already damp when i got it from the bag. I buried the eggs just over 1/2 way into this mix.
The baby took the longest I have ever had a sulcata take for a first pip out of a clutch - 96 days when normally I got 86 days. The yolk sac was substantially smaller than previous hatchlings and was the biggest hatchling I've ever gotten out of this female - 37 grams. The eggshell was quite thin and crumbled in my hand as I took some out to add to the brood box when I took the hatchling out.
I believe both the acidity / humic matter of the peat, along with the better water potential of the media are key things I am watching as this progresses.
Did you measure the pH of your vermiculite/peat mix at the completion of incubation? Suspect it will be similar to pH of straight peat.
Thanks