I have been using diatomite since June in potting up some of my phals, so far so good. I do a mix of 60/40 diatomite/ sphag. I like diatomite because it is very easy to use, free draining, ph neutral, non- organic and water retaining.
I started to use it on my phal seedlings since s/h (LECA) was too cold for the babies in winter. I have tried it on phals, Onc. Sharry Baby and one catt, and I would only use this diatomit/ sphag mix only for phals under my conditons.
My pots are lined with the diatomite at the base and sphag is introduced at a depth to cover the roots with a mixed layer of diatomite.
Some phal growers in Singapore have had geat success in using this potting mix. The porpotions can be adjusted under different conditions.
The people who sold me the diatomite use it with CHC, I guess diatomite is very versatile!