Miltonia/miltoniopsis in volcanic rock - good idea or not?

[mexicowpants]

Oh dear, I'm afraid that's not going to be particularly cool...
Thanks for the input, I'll probably repot it in a coarse bark/sphagnum mix then - I'll just have make sure it's not so tightly packed as on the other one, I think that's what did it in.

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[mexicowpants]

OK, unpotting this one, it seems to have a pretty healthy set of roots but, as I expected, the sphag is very tightly packed. Unfortunately, my cleaning lady decided to water it this morning (despite clear instructions to leave well alone), so I don't really know how well it's been draining.
Here are what the roots currently look like:


Something else that worried me is the (in my opinion) INSANE amount of slow-release fertiliser I found under the top layer of sphag:


This probably explains why the healthiest part of the plant is on the other side of the pot.

My question is now: how to proceed? I want to remove as much of that tightly packed sphag as possible and repot in a bark / sphag mix... How do I do this causing as little damage as possible to the roots?

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[estación seca]

With your heat and dryness, I would not use volcanic rock. You won't be able to water enough. The sphagnum moss is probably your best bet, and the unpotted plant you showed has very healthy roots. I would not remove the old material from this plant and risk damaging its roots going into your even hotter season.

I would pot it in additional sphagnum around the existing root ball. Use a clay pot to take advantage of evaporative cooling. If you can keep the roots cool it will do better in your circumstances. Don't worry about the osmotic release pellets. Don't risk letting this plant dry out in the heat or it will be a goner.