No CaCO3 added to water, though Joe Mazrimas swears by this method (CPN,
ca. 1978) but uses agricultural lime (Ca(OH)2). I remember reading in
CPN that vermiculite is a special soil aeration medium in which the
CaCO3 or Ca(OH)2 can embed or 'hide-out' in its clefts or pores.
Subsequent waterings can leach out the calcium salts into the growing
medium, thereby maintaining a slightly alkaline pH which most Mexican
Pings. seem to appreciate or even need. Thus a combination of alkaline
watering and growing medium MAY be too much for these calciphiles and I
would stick to one technique and not both. He does not place his pots
in trays, as most Mexican Pings need good drainage. Grant waters from
above -very mildly- when necessary, which is about once a week or so in
his naturally humid and cool basement. I should correct my- self from
yesterday's message: P. colimensis will happily grow in BOTH milled
Sphagnum and the peat/vermiculite/CaCO3 mix and not just the former one.
There appears to be certain species - P. colimensis, P. caudata, P.
agnata, P. pachuca and P. ehlersae - which do not favor a certain mix,
but time and further experimentation will tell.
Rob (M.)