You wrote that you wonder if the native soil has a characteristic
which we are not mimicking, ie Ph, Fungal symbiosis or mineral content?
Could it be laterite that is missing in the peat/silica sand mix?
I seem to remember that laterite can be anywhere in western australia.
It is rich in iron, I would experiment adding some laterite into
the potting mix or fertilize it with chelated iron.
Happy growing and trapping.
Cheerio,
Shing.
--- Shing Lam <shlam@hkueee.hku.hk>